linux-kernel - Re: [PATCH v2] cgroup/rstat: change cgroup_base

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Message-ID: <aF7L8jRkWm1TrwSu@slm.duckdns.org>
Date: Fri, 27 Jun 2025 06:50:58 -1000
From: "tj@...nel.org" <tj@...nel.org>
To: "Wlodarczyk, Bertrand" <bertrand.wlodarczyk@...el.com>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"mkoutny@...e.com" <mkoutny@...e.com>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"inwardvessel@...il.com" <inwardvessel@...il.com>
Subject: Re: [PATCH v2] cgroup/rstat: change cgroup_base_stat to atomic

Hello,

On Fri, Jun 27, 2025 at 01:15:31PM +0000, Wlodarczyk, Bertrand wrote:
...
>  > Also the response to the tearing issue explained by JP is not satisfying.
> 
> In other words, the claim is: "it's better to stall other cpus in spinlock plus disable IRQ every time in order to 
> serve outdated snapshot instead of providing user to the freshest statistics much, much faster".
> In term of statistics, freshest data served fast to the user is, in my opinion, better behavior.

This is a false choice, I think. e.g. We can easily use seqlock to remove
strict synchronization only from user side, right?

> I wouldn't be addressing this issue if there were no customers affected by rstat latency in multi-container
> multi-cpu scenarios.

Out of curiosity, can you explain the case that you observed in more detail?
What were the customer doing?

Thanks.

-- 
tejun