Date: Sat, 12 Jul 2014 15:05:38 +0900 From: Yonghyeon PYUN <pyunyh@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: "Russell L. Carter" <rcarter@pinyon.org>, freebsd-net@freebsd.org, Rick Macklem <rmacklem@uoguelph.ca> Subject: Re: NFS client READ performance on -current Message-ID: <20140712060538.GA3649@michelle.fasterthan.com> In-Reply-To: <201407110954.23381.jhb@freebsd.org> References: <1610703198.9975909.1405031503143.JavaMail.root@uoguelph.ca> <201407110954.23381.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Fri, Jul 11, 2014 at 09:54:23AM -0400, John Baldwin wrote: > On Thursday, July 10, 2014 6:31:43 pm Rick Macklem wrote: > > John Baldwin wrote: > > > On Thursday, July 03, 2014 8:51:01 pm Rick Macklem wrote: > > > > Russell L. Carter wrote: > > > > > > > > > > > > > > > On 07/02/14 19:09, Rick Macklem wrote: > > > > > > > > > > > Could you please post the dmesg stuff for the network > > > > > > interface, > > > > > > so I can tell what driver is being used? I'll take a look at > > > > > > it, > > > > > > in case it needs to be changed to use m_defrag(). > > > > > > > > > > em0: <Intel(R) PRO/1000 Network Connection 7.4.2> port > > > > > 0xd020-0xd03f > > > > > mem > > > > > 0xfe4a0000-0xfe4bffff,0xfe480000-0xfe49ffff irq 44 at device 0.0 > > > > > on > > > > > pci2 > > > > > em0: Using an MSI interrupt > > > > > em0: Ethernet address: 00:15:17:bc:29:ba > > > > > 001.000007 [2323] netmap_attach success for em0 tx > > > > > 1/1024 > > > > > rx > > > > > 1/1024 queues/slots > > > > > > > > > > This is one of those dual nic cards, so there is em1 as well... > > > > > > > > > Well, I took a quick look at the driver and it does use m_defrag(), > > > > but > > > > I think that the "retry:" label it does a goto after doing so might > > > > be in > > > > the wrong place. > > > > > > > > The attached untested patch might fix this. > > > > > > > > Is it convenient to build a kernel with this patch applied and then > > > > try > > > > it with TSO enabled? > > > > > > > > rick > > > > ps: It does have the transmit segment limit set to 32. I have no > > > > idea if > > > > this is a hardware limitation. > > > > > > I think the retry is not in the wrong place, but the overhead of all > > > those > > > pullups is apparently quite severe. > > The m_defrag() call after the first failure will just barely squeeze > > the just under 64K TSO segment into 32 mbuf clusters. Then I think any > > m_pullup() done during the retry will allocate an mbuf > > (at a glance it seems to always do this when the old mbuf is a cluster) > > and prepend that to the list. > > --> Now the list is > 32 mbufs again and the bus_dmammap_load_mbuf_sg() > > will fail again on the retry, this time fatally, I think? > > > > I can't see any reason to re-do all the stuff using m_pullup() and Russell > > reported that moving the "retry:" fixed his problem, from what I understood. > > Ah, I had assumed (incorrectly) that the m_pullup()s would all be nops in this > case. It seems the NIC would really like to have all those things in a single > segment, but it is not required, so I agree that your patch is fine. > I recall em(4) controllers have various limitation in TSO. Driver has to update IP header to make TSO work so driver has to get a writable mbufs. bpf(4) consumers will see IP packet length is 0 after this change. I think tcpdump has a compile time option to guess correct IP packet length. The firmware of controller also should be able to access complete IP/TCP header in a single buffer. I don't remember more details in TSO limitation but I guess you may be able to get more details TSO limitation from publicly available Intel data sheet.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20140712060538.GA3649>