lkml.org 
[lkml]   [2020]   [Mar]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] irqchip/gic-v3-its: Balance initial LPI affinity across CPUs
Hi John,

On 2020-03-12 15:41, John Garry wrote:
> On 12/03/2020 11:55, Marc Zyngier wrote:
>
> Hi Marc,
>
>> When mapping a LPI, the ITS driver picks the first possible
>> affinity, which is in most cases CPU0, assuming that if
>> that's not suitable, someone will come and set the affinity
>> to something more interesting.
>>
>> It apparently isn't the case, and people complain of poor
>> performance when many interrupts are glued to the same CPU.
>> So let's place the interrupts by finding the "least loaded"
>> CPU (that is, the one that has the fewer LPIs mapped to it).
>> So called 'managed' interrupts are an interesting case where
>> the affinity is actually dictated by the kernel itself, and
>> we should honor this.
>>
>> Reported-by: John Garry <john.garry@huawei.com>
>> Link:
>> https://lore.kernel.org/r/1575642904-58295-1-git-send-email-john.garry@huawei.com
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> Cc: John Garry <john.garry@huawei.com>
>> Cc: Ming Lei <ming.lei@redhat.com>
>> ---
>> Reviving this at John's request.
>
> Thanks very much. I may request a colleague test this due to possible
> precautionary office closure.

Huh. Not great... :-(

>
> The major change is that the
>> affinity follows the x86 model, as described by Thomas.
>
> There seems to be a subtle difference between this implementation and
> what Thomas described for managed interrupts handling on x86. That
> being, managed interrupt loading is counted separately to total
> interrupts per CPU for x86. That seems quite important so that we
> spread managed interrupts evenly.

Hmmm. Yes. That'd require a separate per-CPU counter. Nothing too
invasive
though. I'll roll that in soon. I still wonder about interaction of
collocated
managed and non-managed interrupts, but we can cross that bridge later.

>> I expect this to have an impact on platforms like D05, where
>> the SAS driver cannot use managed affinity just yet.
>
> I need some blk-mq and SCSI changes to go in first to improve the
> interrupt handling there, hopefully we can make progress on that soon.

That'd be good.

Thanks,

M.
--
Jazz is not dead. It just smells funny...

\
 
 \ /
  Last update: 2022-09-17 16:07    [W:0.371 / U:0.172 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site