Date: Fri, 01 Jun 2007 00:12:39 -0600 From: Scott Long <scottl@samsco.org> To: Hidetoshi Shimokawa <simokawa@FreeBSD.ORG> Cc: freebsd-scsi@FreeBSD.ORG Subject: Re: scsi_target with multiple luns Message-ID: <465FB8D7.9010102@samsco.org> In-Reply-To: <626eb4530705312300n177e677cyac2e8ba69039160d@mail.gmail.com> References: <86tztspdil.wl%simokawa@FreeBSD.ORG> <465F955E.7050103@samsco.org> <7579f7fb0705312147p60255cf2r9eac5d5eb8aa5236@mail.gmail.com> <626eb4530705312300n177e677cyac2e8ba69039160d@mail.gmail.com>
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Many companies use the scsi_target and targ code as a basis for prototyping and developing target code that is more suited to their needs. Scott Hidetoshi Shimokawa wrote: > Yes, scsi_target(8) is an example. > But the problem I described is actually a problem of targ(4) > (scsi_target.c). > The userland can do nothing about this problem. > Or do you mean targ(4) is also an example? > > On 6/1/07, Matthew Jacob <lydianconcepts@gmail.com> wrote: >> Remember that scsi_target is an example. A fine example, but an >> example. Having a single user process that can be shot and killed, no >> matter how multithreaded or AIO'd, is not necessarily the wisest >> choice for building a target device. >> >> >> On 5/31/07, Scott Long <scottl@samsco.org> wrote: >> > Hidetoshi Shimokawa wrote: >> > > I have not fully analyzed the problem but I'll describe it just >> for a note. >> > > I'd like to ask maintainers of scsi_target for further analysis. >> > > >> > > I experiance a problem with small number(1) of simq and multiple >> > > scsi_target(8) instances. >> > > >> > > As far as I understand, the following situation could occur under >> a fairly >> > > heavy load. >> > > >> > > 1. process A send a request -> cam send to sim >> > > 2. process B send a request -> blocked because the simq is full >> > > 3. the request of process A is finished (in the context of process A) >> > > 4. cam/scsi_target tries to send the request of process B. >> > > But the mapped memory is of process A, and scsi_target send wrong >> > > ccb to sim. >> > > >> > > Maybe, we should rewrite scsi_target in kernel space with GEOM >> support.. >> > >> > I'm unclear on how GEOM would fix this. Also, scsi targets aren't >> > always DA devices. I dedicated scsi_da_target device that is backed >> > by GEOM might be interesting, though. Even more interesting would be >> > a direct DMA method that required no KVA mappings for the data. >> > >> > Scott >> > >> > _______________________________________________ >> > freebsd-scsi@freebsd.org mailing list >> > http://lists.freebsd.org/mailman/listinfo/freebsd-scsi >> > To unsubscribe, send any mail to "freebsd-scsi-unsubscribe@freebsd.org" >> > >> >> > >
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