[BUG,REGRESSION?] 3.11.6+,3.12: GbE iface rate drops to few KB/s
Arnaud Ebalard
arno at natisbad.org
Wed Nov 20 14:26:16 EST 2013
Hi,
Willy Tarreau <w at 1wt.eu> writes:
> first, thanks for all these tests.
>
> On Wed, Nov 20, 2013 at 12:53:43AM +0100, Arnaud Ebalard wrote:
> (...)
>> In the end, here are the conclusions *I* draw from this test session,
>> do not hesitate to correct me:
>>
>> - Eric, it seems something changed in linus tree betwen the beginning
>> of the thread and now, which somehow reduces the effect of the
>> regression we were seen: I never got back the 256KB/s.
>> - You revert patch still improves the perf a lot
>> - It seems reducing MVNETA_TX_DONE_TIMER_PERIOD does not help
>> - w/ your revert patch, I can confirm that mvneta driver is capable of
>> doing line rate w/ proper tweak of TCP send window (256KB instead of
>> 4M)
>> - It seems I will I have to spend some time on the SATA issues I
>> previously thought were an artefact of not cleaning my tree during a
>> debug session [1], i.e. there is IMHO an issue.
>
> Could you please try Eric's patch that was just merged into Linus' tree
> if it was not yet in the kernel you tried :
>
> 98e09386c0e tcp: tsq: restore minimal amount of queueing
I have it in my quilt set.
> For me it restored the original performance (I saturate the Gbps with
> about 7 concurrent streams).
>
> Further, I wrote the small patch below for mvneta. I'm not sure it's
> smp-safe but it's a PoC. In mvneta_poll() which currently is only called
> upon Rx interrupt, it tries to flush all possible remaining Tx descriptors
> if any. That significantly improved my transfer rate, now I easily achieve
> 1 Gbps using a single TCP stream on the mirabox. Not tried on the AX3 yet.
>
> It also increased the overall connection rate by 10% on empty HTTP responses
> (small packets), very likely by reducing the dead time between some segments!
>
> You'll probably want to give it a try, so here it comes.
hehe, I was falling short of patches to test tonight ;-) I will give it
a try now.
Cheers,
a+
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