From: Eric Dumazet <eric.dumazet@gmail.com>
To: Saeed Mahameed <saeedm@mellanox.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
Tariq Toukan <tariqt@mellanox.com>,
"xiyou.wangcong@gmail.com" <xiyou.wangcong@gmail.com>
Subject: Re: [Patch net-next] mlx5: use RCU lock in mlx5_eq_cq_get()
Date: Wed, 6 Feb 2019 09:17:17 -0800 [thread overview]
Message-ID: <8df59337-8c20-de92-6088-d008031da6f2@gmail.com> (raw)
In-Reply-To: <e88ac12b80b510648f7ab1d4cee50c43908ba49d.camel@mellanox.com>
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.
next prev parent reply other threads:[~2019-02-06 17:17 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-06 0:35 [Patch net-next] mlx5: use RCU lock in mlx5_eq_cq_get() Cong Wang
2019-02-06 12:02 ` Tariq Toukan
2019-02-06 16:55 ` Saeed Mahameed
2019-02-06 17:15 ` Cong Wang
2019-02-06 17:35 ` Saeed Mahameed
2019-02-06 17:43 ` Cong Wang
2019-02-06 17:17 ` Eric Dumazet [this message]
2019-02-06 17:37 ` Saeed Mahameed
2019-02-06 17:35 ` Saeed Mahameed
2019-02-06 17:40 ` Saeed Mahameed
2019-02-06 22:51 ` Cong Wang
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