linux-kernel - Re: [External] Re: [PATCH] cgroup: rstat: Simplified cgroup_base_stat_flush() update last

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Message-ID: <d6d19a61-a584-1839-e6cc-ea63479ca800@bytedance.com>
Date:   Mon, 12 Jun 2023 11:13:41 +0800
From:   Hao Jia <jiahao.os@...edance.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     tj@...nel.org, lizefan.x@...edance.com, hannes@...xchg.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH] cgroup: rstat: Simplified
 cgroup_base_stat_flush() update last_bstat logic



On 2023/5/24 Michal Koutný wrote:
> On Wed, May 24, 2023 at 02:54:10PM +0800, Hao Jia <jiahao.os@...edance.com> wrote:
>> Yes, so we need @curr to record the bstat value after the sequence fetch is
>> completed.
> 
> No, I still don't see a problem that it solves. If you find incorrect
> data being reported, please explain it more/with an example.
> 
>> Yes, but it may not be obvious.
>> Another reason is that when we complete an update, we snapshot last_bstat as
>> the current bstat, which is better for readers to understand. Arithmetics is
>> somewhat obscure.
> 
> The readability here is subjective. It'd be interesting to have some
> data comparing arithmetics vs copying though.
> 

Sorry for replying you so late. I am using RDTSC on my machine (an Intel 
Xeon(R) Platinum 8260 CPU@...0GHz machine with 2 NUMA nodes each of 
which has 24 cores with SMT2 enabled, so 96 CPUs in total.) to compare 
the time consumption of arithmetics vs copying. There is almost no 
difference in the time consumption between arithmetics and copying.



> HTH,
> Michal