linux-kernel - Re: [PATCH] net/mlx5: Added cond

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Message-ID: <1d9d555f-33b7-4d95-8fbd-87709386583c@intel.com>
Date: Fri, 23 Aug 2024 06:08:19 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Mohamed Khalfella <mkhalfella@...estorage.com>, Moshe Shemesh
	<moshe@...dia.com>
CC: Yuanyuan Zhong <yzhong@...estorage.com>, Saeed Mahameed
	<saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>, Tariq Toukan
	<tariqt@...dia.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Shay Drori <shayd@...dia.com>, <netdev@...r.kernel.org>,
	<linux-rdma@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net/mlx5: Added cond_resched() to crdump collection

On 8/22/24 19:08, Mohamed Khalfella wrote:
> On 2024-08-22 09:40:21 +0300, Moshe Shemesh wrote:
>>
>>
>> On 8/21/2024 1:27 AM, Mohamed Khalfella wrote:
>>>
>>> On 2024-08-20 12:09:37 +0200, Przemek Kitszel wrote:
>>>> On 8/19/24 23:42, Mohamed Khalfella wrote:


>>>
>>> Putting a cond_resched() every 16 register reads, similar to
>>> mlx5_vsc_wait_on_flag(), should be okay. With the numbers above, this
>>> will result in cond_resched() every ~0.56ms, which is okay IMO.
>>
>> Sorry for the late response, I just got back from vacation.
>> All your measures looks right.
>> crdump is the devlink health dump of mlx5 FW fatal health reporter.
>> In the common case since auto-dump and auto-recover are default for this
>> health reporter, the crdump will be collected on fatal error of the mlx5
>> device and the recovery flow waits for it and run right after crdump
>> finished.
>> I agree with adding cond_resched(), but I would reduce the frequency,
>> like once in 1024 iterations of register read.
>> mlx5_vsc_wait_on_flag() is a bit different case as the usleep there is
>> after 16 retries waiting for the value to change.
>> Thanks.
> 
> Thanks for taking a look. Once in every 1024 iterations approximately
> translates to 35284.4ns * 1024 ~= 36.1ms, which is relatively long time
> IMO. How about any power-of-two <= 128 (~4.51ms)?

Such tune-up would matter for interactive use of the machine with very
little cores, is that the case? Otherwise I see no point [to make it
overall a little slower, as that is the tradeoff].