Date: Wed, 18 Nov 2015 11:05:03 -0500 From: "Kenneth D. Merry" <ken@FreeBSD.ORG> To: scsi@freebsd.org, current@freebsd.org Subject: Re: async pass(4) patches available Message-ID: <20151118160503.GA3095@mithlond.kdm.org> In-Reply-To: <20150330222358.GA46342@mithlond.kdm.org> References: <20150330222358.GA46342@mithlond.kdm.org>
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--pWyiEgJYm5f9v55/ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline I have updated the asynchronous pass(4) changes, and fixed a number of bugs in camdd(8). The new patches are here: FreeBSD/head as of SVN revision 290970: http://people.freebsd.org/~ken/async_pass.head.20151117.1.txt FreeBSD stable/10 as of SVN revision 290899: http://people.freebsd.org/~ken/async_pass.stable10.20151117.1.txt And a description / draft commit message, this time updated to include all the files that have changed: http://people.freebsd.org/~ken/async_pass_commitmsg.20151118.txt I have also attached the description to this email. At this point I think I've fixed enough bugs and it is stable enough to go into the tree. That will allow others to more easily use the code and add enhancements. Ken On Mon, Mar 30, 2015 at 16:23:58 -0600, Kenneth D. Merry wrote: > > I have put patches to add an asynchronous interface to the pass(4) driver > and add a new camdd(8) utility here: > > FreeBSD/head as of SVN revision 280857: > > http://people.freebsd.org/~ken/async_pass.head.20150330.1.txt > > FreeBSD stable/10 as of SVN revision 280856: > > http://people.freebsd.org/~ken/async_pass.stable_10.20150330.1.txt > > And the description / draft commit message: > > http://people.freebsd.org/~ken/async_pass_commitmsg.20150330.txt > > I have also attached the description and draft commit message to this > email. > > The asynchronous changes to the pass(4) driver allow queueing and fetching > CAM CCBs via two new ioctls. Notification of completed I/O can come via > kqueue(2), poll(2), select(2), etc. > > The camdd(8) utility is intended as a simple data transfer utility, > benchmark, and an in-tree example of how to use the asynchronous pass(4) > interface. > > camdd(8) is still a work in progress. It needs to be cleaned up a bit and > streamlined. > > There is one known arrival and departure bug with the pass(4) driver > changes. We've reproduced it with our tests at Spectra, but I haven't yet > tracked it down. > > There are many more arrival and departure bugs in FreeBSD/head, however. > We have fixed quite a few in our local tree, but the test (called devad2) > that triggers all of the problems uses the asynchronous pass(4) interface. > So this is a prerequisite for fixing/verifying those bugs. > > Comments and testing are welcome! As I said, camdd(8) in particular is a > work in progress. It could use some cleanup and there are some more useful > features that could be added there. > > Part of the reason for camdd(8) was as a test facility for the new > interface. But, it also serves as a useful demonstration of the > asynchronous pass(4) functionality, given that the original application > that used the API doesn't make sense to go into FreeBSD. (It is > Spectra-specific, and not generally useful.) > > Ken > -- > Kenneth Merry > ken@FreeBSD.ORG > Add asynchronous command support to the pass(4) driver, and the new > camdd(8) utility. > > CCBs may be queued to the driver via the new CAMIOQUEUE ioctl, and > completed CCBs may be retrieved via the CAMIOGET ioctl. User > processes can use poll(2) or kevent(2) to get notification when > I/O has completed. > > While the existing CAMIOCOMMAND blocking ioctl interface only > supports user virtual data pointers in a CCB (generally only > one per CCB), the new CAMIOQUEUE ioctl supports user virtual and > physical address pointers, as well as user virtual and physical > scatter/gather lists. This allows user applications to have more > flexibility in their data handling operations. > > Kernel memory for data transferred via the queued interface is > allocated from the zone allocator in MAXPHYS sized chunks, and user > data is copied in and out. This is likely faster than the > vmapbuf()/vunmapbuf() method used by the CAMIOCOMMAND ioctl in > configurations with many processors (there are more TLB shootdowns > caused by the mapping/unmapping operation) but may not be as fast > as running with unmapped I/O. > > The new memory handling model for user requests also allows > applications to send CCBs with request sizes that are larger than > MAXPHYS. The pass(4) driver now limits queued requests to the I/O > size listed by the SIM driver in the maxio field in the Path > Inquiry (XPT_PATH_INQ) CCB. > > There are some things things would be good to add: > > 1. Come up with a way to do unmapped I/O on multiple buffers. > Currently the unmapped I/O interface operates on a struct bio, > which includes only one address and length. It would be nice > to be able to send an unmapped scatter/gather list down to > busdma. This would allow eliminating the copy we currently do > for data. > > 2. Add an ioctl to list currently outstanding CCBs in the various > queues. > > 3. Add an ioctl to cancel a request, or use the XPT_ABORT CCB to do > that. > > 4. Test physical address support. Virtual pointers and scatter > gather lists have been tested, but I have not yet tested > physical addresses or scatter/gather lists. > > 5. Investigate multiple queue support. At the moment there is one > queue of commands per pass(4) device. If multiple processes > open the device, they will submit I/O into the same queue and > get events for the same completions. This is probably the right > model for most applications, but it would be good to make sure > that there is not really a case for multiple queues before > pushing this code upstream. > > Also, add a new utility, camdd(8) that uses the asynchronous pass(4) > driver interface. > > This utility is intended to be a basic data transfer/copy utility, > a simple benchmark utility, and an example of how to use the > asynchronous pass(4) interface. > > It can copy data to and from pass(4) devices using any target queue > depth, starting offset and blocksize for the input and ouptut devices. > It currently only supports SCSI devices, but could be easily extended > to support ATA devices. > > It can also copy data to and from regular files, block devices, tape > devices, pipes, stdin, and stdout. It does not support queueing > multiple commands to any of those targets, since it uses the standard > read(2)/write(2)/writev(2)/readv(2) system calls. > > The I/O is done by two threads, one for the reader and one for the > writer. The reader thread sends completed read requests to the > writer thread in strictly sequential order, even if they complete > out of order. That could be modified later on for random I/O patterns > or slightly out of order I/O. > > camdd(8) uses kqueue(2)/kevent(2) to get I/O compeltion events from > the pass(4) driver and also to send request notifications internally. > > For pass(4) devcies, camdd(8) uses a single buffer (CAM_DATA_VADDR) > per CAM CCB on the reading side, and a scatter/gather list > (CAM_DATA_SG) on the writing side. In addition to testing both > interfaces, this makes any potential reblocking of I/O easier. No > data is copied between the reader and the writer, but rather the > reader's buffers are split into multiple I/O requests or combined > into a single I/O request depending on the input and output blocksize. > > For the file I/O path, camdd(8) also uses a single buffer (read(2), > write(2), pread(2) or pwrite(2)) on reads, and a scatter/gather list > (readv(2), writev(2), preadv(2), pwritev(2)) on writes. > > Things that would be nice to do for camdd(8) eventually: > > 1. Add support for I/O pattern generation. Patterns like all > zeros, all ones, LBA-based patterns, random patterns, etc. Right > Now you can always use /dev/zero, /dev/random, etc. > > 2. Add support for a "sink" mode, so we do only reads with no > writes. Right now, you can use /dev/null. > > 3. Add support for automatic queue depth probing, so that we can > figure out the right queue depth on the input and output side > for maximum throughput. At the moment it defaults to 6. > > 4. Add support for SATA device passthrough I/O. > > 5. Add support for random LBAs and/or lengths on the input and > side. > > 6. Track average per-I/O latency and busy time. The busy time > and latency could also feed in to the automatic queue depth > determination. > > sys/cam/scsi/scsi_pass.h: > Define two new ioctls, CAMIOQUEUE and CAMIOGET, that queue > and fetch asynchronous CAM CCBs respectively. > > Although these ioctls do not have a declared argument, they > both take a union ccb pointer. If we declare a size here, > the ioctl code in sys/kern/sys_generic.c will malloc and free > a buffer for either the CCB or the CCB pointer (depending on > how it is declared). Since we have to keep a copy of the > CCB (which is fairly large) anyway, having the ioctl malloc > and free a CCB for each call is wasteful. > > sys/cam/scsi/scsi_pass.c: > Add asynchronous CCB support. > > Add two new ioctls, CAMIOQUEUE and CAMIOGET. > > CAMIOQUEUE adds a CCB to the incoming queue. The CCB is > executed immediately (and moved to the active queue) if it > is an immediate CCB, but otherwise it will be executed > in passstart() when a CCB is available from the transport layer. > > When CCBs are completed (because they are immediate or > passdone() if they are queued), they are put on the done > queue. > > If we get the final close on the device before all pending > I/O is complete, all active I/O is moved to the abandoned > queue and we increment the peripheral reference count so > that the peripheral driver instance doesn't go away before > all pending I/O is done. > > The new passcreatezone() function is called on the first > call to the CAMIOQUEUE ioctl on a given device to allocate > the UMA zones for I/O requests and S/G list buffers. This > may be good to move off to a taskqueue at some point. > The new passmemsetup() function allocates memory and > scatter/gather lists to hold the user's data, and copies > in any data that needs to be written. For virtual pointers > (CAM_DATA_VADDR), the kernel buffer is malloced from the > new pass(4) driver malloc bucket. For virtual > scatter/gather lists (CAM_DATA_SG), buffers are allocated > from a new per-pass(9) UMA zone in MAXPHYS-sized chunks. > Physical pointers are passed in unchanged. We have support > for up to 16 scatter/gather segments (for the user and > kernel S/G lists) in the default struct pass_io_req, so > requests with longer S/G lists require an extra kernel malloc. > > The new passcopysglist() function copies a user scatter/gather > list to a kernel scatter/gather list. The number of elements > in each list may be different, but (obviously) the amount of data > stored has to be identical. > > The new passmemdone() function copies data out for the > CAM_DATA_VADDR and CAM_DATA_SG cases. > > The new passiocleanup() function restores data pointers in > user CCBs and frees memory. > > Add new functions to support kqueue(2)/kevent(2): > > passreadfilt() tells kevent whether or not the done > queue is empty. > > passkqfilter() adds a knote to our list. > > passreadfiltdetach() removes a knote from our list. > > Add a new function, passpoll(), for poll(2)/select(2) > to use. > > Add devstat(9) support for the queued CCB path. > > usr.sbin/camdd/Makefile: > Add a makefile for camdd(8). > > usr.sbin/camdd/camdd.8: > Man page for camdd(8). > > usr.sbin/camdd/camdd.c: > The new camdd(8) utility. > -- Kenneth Merry ken@FreeBSD.ORG --pWyiEgJYm5f9v55/ Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="async_pass_commitmsg.20151118.txt" Add asynchronous command support to the pass(4) driver, and the new camdd(8) utility. CCBs may be queued to the driver via the new CAMIOQUEUE ioctl, and completed CCBs may be retrieved via the CAMIOGET ioctl. User processes can use poll(2) or kevent(2) to get notification when I/O has completed. While the existing CAMIOCOMMAND blocking ioctl interface only supports user virtual data pointers in a CCB (generally only one per CCB), the new CAMIOQUEUE ioctl supports user virtual and physical address pointers, as well as user virtual and physical scatter/gather lists. This allows user applications to have more flexibility in their data handling operations. Kernel memory for data transferred via the queued interface is allocated from the zone allocator in MAXPHYS sized chunks, and user data is copied in and out. This is likely faster than the vmapbuf()/vunmapbuf() method used by the CAMIOCOMMAND ioctl in configurations with many processors (there are more TLB shootdowns caused by the mapping/unmapping operation) but may not be as fast as running with unmapped I/O. The new memory handling model for user requests also allows applications to send CCBs with request sizes that are larger than MAXPHYS. The pass(4) driver now limits queued requests to the I/O size listed by the SIM driver in the maxio field in the Path Inquiry (XPT_PATH_INQ) CCB. There are some things things would be good to add: 1. Come up with a way to do unmapped I/O on multiple buffers. Currently the unmapped I/O interface operates on a struct bio, which includes only one address and length. It would be nice to be able to send an unmapped scatter/gather list down to busdma. This would allow eliminating the copy we currently do for data. 2. Add an ioctl to list currently outstanding CCBs in the various queues. 3. Add an ioctl to cancel a request, or use the XPT_ABORT CCB to do that. 4. Test physical address support. Virtual pointers and scatter gather lists have been tested, but I have not yet tested physical addresses or scatter/gather lists. 5. Investigate multiple queue support. At the moment there is one queue of commands per pass(4) device. If multiple processes open the device, they will submit I/O into the same queue and get events for the same completions. This is probably the right model for most applications, but it would be good to make sure that there is not really a case for multiple queues before pushing this code upstream. Also, add a new utility, camdd(8) that uses the asynchronous pass(4) driver interface. This utility is intended to be a basic data transfer/copy utility, a simple benchmark utility, and an example of how to use the asynchronous pass(4) interface. It can copy data to and from pass(4) devices using any target queue depth, starting offset and blocksize for the input and ouptut devices. It currently only supports SCSI devices, but could be easily extended to support ATA devices. It can also copy data to and from regular files, block devices, tape devices, pipes, stdin, and stdout. It does not support queueing multiple commands to any of those targets, since it uses the standard read(2)/write(2)/writev(2)/readv(2) system calls. The I/O is done by two threads, one for the reader and one for the writer. The reader thread sends completed read requests to the writer thread in strictly sequential order, even if they complete out of order. That could be modified later on for random I/O patterns or slightly out of order I/O. camdd(8) uses kqueue(2)/kevent(2) to get I/O completion events from the pass(4) driver and also to send request notifications internally. For pass(4) devcies, camdd(8) uses a single buffer (CAM_DATA_VADDR) per CAM CCB on the reading side, and a scatter/gather list (CAM_DATA_SG) on the writing side. In addition to testing both interfaces, this makes any potential reblocking of I/O easier. No data is copied between the reader and the writer, but rather the reader's buffers are split into multiple I/O requests or combined into a single I/O request depending on the input and output blocksize. For the file I/O path, camdd(8) also uses a single buffer (read(2), write(2), pread(2) or pwrite(2)) on reads, and a scatter/gather list (readv(2), writev(2), preadv(2), pwritev(2)) on writes. Things that would be nice to do for camdd(8) eventually: 1. Add support for I/O pattern generation. Patterns like all zeros, all ones, LBA-based patterns, random patterns, etc. Right Now you can always use /dev/zero, /dev/random, etc. 2. Add support for a "sink" mode, so we do only reads with no writes. Right now, you can use /dev/null. 3. Add support for automatic queue depth probing, so that we can figure out the right queue depth on the input and output side for maximum throughput. At the moment it defaults to 6. 4. Add support for SATA device passthrough I/O. 5. Add support for random LBAs and/or lengths on the input and side. 6. Track average per-I/O latency and busy time. The busy time and latency could also feed in to the automatic queue depth determination. sys/cam/scsi/scsi_pass.h: Define two new ioctls, CAMIOQUEUE and CAMIOGET, that queue and fetch asynchronous CAM CCBs respectively. Although these ioctls do not have a declared argument, they both take a union ccb pointer. If we declare a size here, the ioctl code in sys/kern/sys_generic.c will malloc and free a buffer for either the CCB or the CCB pointer (depending on how it is declared). Since we have to keep a copy of the CCB (which is fairly large) anyway, having the ioctl malloc and free a CCB for each call is wasteful. sys/cam/scsi/scsi_pass.c: Add asynchronous CCB support. Add two new ioctls, CAMIOQUEUE and CAMIOGET. CAMIOQUEUE adds a CCB to the incoming queue. The CCB is executed immediately (and moved to the active queue) if it is an immediate CCB, but otherwise it will be executed in passstart() when a CCB is available from the transport layer. When CCBs are completed (because they are immediate or passdone() if they are queued), they are put on the done queue. If we get the final close on the device before all pending I/O is complete, all active I/O is moved to the abandoned queue and we increment the peripheral reference count so that the peripheral driver instance doesn't go away before all pending I/O is done. The new passcreatezone() function is called on the first call to the CAMIOQUEUE ioctl on a given device to allocate the UMA zones for I/O requests and S/G list buffers. This may be good to move off to a taskqueue at some point. The new passmemsetup() function allocates memory and scatter/gather lists to hold the user's data, and copies in any data that needs to be written. For virtual pointers (CAM_DATA_VADDR), the kernel buffer is malloced from the new pass(4) driver malloc bucket. For virtual scatter/gather lists (CAM_DATA_SG), buffers are allocated from a new per-pass(9) UMA zone in MAXPHYS-sized chunks. Physical pointers are passed in unchanged. We have support for up to 16 scatter/gather segments (for the user and kernel S/G lists) in the default struct pass_io_req, so requests with longer S/G lists require an extra kernel malloc. The new passcopysglist() function copies a user scatter/gather list to a kernel scatter/gather list. The number of elements in each list may be different, but (obviously) the amount of data stored has to be identical. The new passmemdone() function copies data out for the CAM_DATA_VADDR and CAM_DATA_SG cases. The new passiocleanup() function restores data pointers in user CCBs and frees memory. Add new functions to support kqueue(2)/kevent(2): passreadfilt() tells kevent whether or not the done queue is empty. passkqfilter() adds a knote to our list. passreadfiltdetach() removes a knote from our list. Add a new function, passpoll(), for poll(2)/select(2) to use. Add devstat(9) support for the queued CCB path. sys/cam/ata/ata_da.c: Add support for the BIO_VLIST bio type. sys/cam/cam_ccb.h: Add a new enumeration for the xflags field in the CCB header. (This doesn't change the CCB header, just adds an enumeration to use.) sys/cam/cam_xpt.c: Add a new function, xpt_setup_ccb_flags(), that allows specifying CCB flags. sys/cam/cam_xpt.h: Add a prototype for xpt_setup_ccb_flags(). sys/cam/scsi/scsi_da.c: Add support for BIO_VLIST. sys/dev/md/md.c: Add BIO_VLIST support to md(4). sys/geom/geom_disk.c: sys/kern/subr_bus_dma.c: Change _bus_dmamap_load_vlist() to take a starting offset and length. Add a new function, _bus_dmamap_load_pages(), that will load a list of physical pages starting at an offset. Update _bus_dmamap_load_bio() to allow loading BIO_VLIST bios. Allow unmapped I/O to start at an offset. sys/kern/subr_uio.c: Add two new functions, physcopyin_vlist() and physcopyout_vlist(). sys/sys/bio.h: Add a new bio flag, BIO_VLIST. sys/sys/uio.h: Add prototypes for physcopyin_vlist() and physcopyout_vlist(). share/man/man4/pass.4: Document the CAMIOQUEUE and CAMIOGET ioctls. usr.sbin/Makefile: Add camdd. usr.sbin/camdd/Makefile: Add a makefile for camdd(8). usr.sbin/camdd/camdd.8: Man page for camdd(8). usr.sbin/camdd/camdd.c: The new camdd(8) utility. --pWyiEgJYm5f9v55/--
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