Date: Tue, 8 Nov 2011 11:53:55 -0700 From: Jason Wolfe <nitroboost@gmail.com> To: Hooman Fazaeli <hoomanfazaeli@gmail.com> Cc: pyunyh@gmail.com, freebsd-net@freebsd.org, Jack Vogel <jfvogel@gmail.com>, Emil Muratov <gpm@hotplug.ru> Subject: Re: Intel 82574L interface wedging on em 7.1.9/7.2.3 when MSIX enabled Message-ID: <CAAAm0r1g=Jgx4REFRWQkhNCYh5M9=hBKK%2Bh5F=Jx7iuZvoTVfQ@mail.gmail.com> In-Reply-To: <4EB96511.50701@gmail.com> References: <CAAAm0r0RXEJo4UiKS=Ui0e5OQTg6sg-xcYf3mYB5%2Bvk8i8557w@mail.gmail.com> <4E8F157A.40702@sentex.net> <CAAAm0r2JH43Rct7UxQK2duH1p43Nepnj5mpb6bXo==DPayhJLg@mail.gmail.com> <4E8F51D4.1060509@sentex.net> <CACqU3MVwLaepFymZJkaVk6p=SpykGhqs=VYFjLh9fP9S=AxDhg@mail.gmail.com> <CAAAm0r1DKvoL9=Ket9up=4%2B5xiCzTTZJK99FhF9jcCA28B0M%2BA@mail.gmail.com> <CAAAm0r3XdsMHZh%2BP_NF-txZasdExzwZ8ymmGQgGhJQds0fOiBQ@mail.gmail.com> <CAAAm0r1iS3z-7CBJ=xYDf%2BJOA1Q2nU0O54Twbyb7FjvgWHjKVw@mail.gmail.com> <4EA7E203.3020306@sepehrs.com> <CAAAm0r3Nr2t8cCetPkFnLQ-3KwqHw_0SpqbtvYPRUkSP=9n8CA@mail.gmail.com> <4EA80818.3030504@sentex.net> <4EA80F88.4000400@hotplug.ru> <4EA82715.2000404@gmail.com> <4EA8FA40.7010504@hotplug.ru> <4EA91836.2040508@gmail.com> <4EA959EE.2070806@hotplug.ru> <4EAD116A.8090006@gmail.com> <CAAAm0r3qm=nQQuAmZDD4k4X8K-xW6_kM9TukRT=1GoG9dYR3zw@mail.gmail.com> <4EAE58A2.9040803@gmail.com> <CAAAm0r0uoPPEQbq5rHkFr6ZLp-WJ4YVjDVvxxV6y%2BUh4eEKDEA@mail.gmail.com> <4EB96511.50701@gmail.com>
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On Tue, Nov 8, 2011 at 10:21 AM, Hooman Fazaeli <hoomanfazaeli@gmail.com>wrote: > I have allocated more time to the problem and guess I can explain what > your problem is. > > With MSIX disabled, the driver uses fast interrupt handler (em_irq_fast) > which calls rx/tx task and then checks for link status change. This > implies that rx/tx task is executed with every link state change. This is > not efficient, as it is a waste of time to start transmission when link is > down. > However, it has the effect that after a temporary link loss > (active->inactive->active), > _start is executed and transmission continues normally. The value of > link_toggles (3) > clearly indicates that you had such a transition when the problem occured. > > With MSIX enabled, the link task (em_handle_link) does _not_ triggers > _start when the link changes state from inactive to active (which it > should). > If if_snd quickly fills up during a temporary link loss, transmission is > stopped forever and the driver never recovers from that state. > > The last patch should have reduced the frequency of the problem > but it assumes every IFQ_ENQUEUE is followed by a if_start which > is not a true assumption. > > If you are willing to test, I can prepare another patch for you to fix > the issue in a different and more reliable way. > > Hooman, Thanks again for the assist, it sounds like this may also be why we see a bit higher latency with MSI-X disabled on this chipset. I'm happy to test any patches as I have a handful of boxes set aside to 'research' this issue. Hopefully the testing here helps along any patches to the tree for others benefit also. Jason
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