On 02/06/2019 08:55 AM, Saeed Mahameed wrote:
> On Wed, 2019-02-06 at 12:02 +0000, Tariq Toukan wrote:
>>
>> On 2/6/2019 2:35 AM, Cong Wang wrote:
>>> mlx5_eq_cq_get() is called in IRQ handler, the spinlock inside
>>> gets a lot of contentions when we test some heavy workload
>>> with 60 RX queues and 80 CPU's, and it is clearly shown in the
>>> flame graph.
>>>
>
>
> Hi Cong,
>
> The patch is ok to me, but i really doubt that you can hit a contention
> on latest upstream driver, since we already have spinlock per EQ, which
> means spinlock per core, each EQ (core) msix handler can only access
> one spinlock (its own), so I am surprised how you got the contention,
> Maybe you are not running on latest upstream driver ?
>
> what is the workload ?
Surprisingly (or not), atomic operations, even on _not_ contended cache lines
can
stall the cpu enough for perf tools to notice...
If the atomic operation can be trivially replaced by RCU, then do it by any
mean.
