From: Oleg Nesterov <oleg@redhat.com>
To: Zheng Zucheng <zhengzucheng@huawei.com>
Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
bristot@redhat.com, vschneid@redhat.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 -next] sched/cputime: Fix mul_u64_u64_div_u64() precision for cputime
Date: Fri, 26 Jul 2024 15:04:01 +0200 [thread overview]
Message-ID: <20240726130401.GB21542@redhat.com> (raw)
In-Reply-To: <20240726104429.GA21542@redhat.com>
On 07/26, Oleg Nesterov wrote:
>
> On 07/26, Zheng Zucheng wrote:
> >
> > before call mul_u64_u64_div_u64(),
> > stime = 175136586720000, rtime = 135989749728000, utime = 1416780000.
>
> So stime + utime == 175138003500000
>
> > after call mul_u64_u64_div_u64(),
> > stime = 135989949653530
>
> Hmm. On x86 mul_u64_u64_div_u64(175136586720000, 135989749728000, 175138003500000)
> returns 135989749728000 == rtime, see below.
Seriously, can you re-check your numbers? it would be nice to understand why
x86_64 differs...
> But perhaps it makes sense to improve the accuracy of mul_u64_u64_div_u64() ?
> See the new() function in the code below.
Just in case, the usage of ilog2 can be improved, but this is minor.
Oleg.
next prev parent reply other threads:[~2024-07-26 13:05 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-07-25 12:03 [PATCH -next] sched/cputime: Fix mul_u64_u64_div_u64() precision for cputime Zheng Zucheng
2024-07-25 14:05 ` Peter Zijlstra
2024-07-25 14:49 ` zhengzucheng
2024-07-25 15:14 ` Peter Zijlstra
2024-07-26 2:32 ` [PATCH v2 " Zheng Zucheng
2024-07-26 10:44 ` Oleg Nesterov
2024-07-26 13:04 ` Oleg Nesterov [this message]
2024-07-26 13:08 ` Peter Zijlstra
2024-07-26 13:30 ` Oleg Nesterov
2024-07-30 6:55 ` Uwe Kleine-König
2024-07-29 10:34 ` [tip: sched/core] " tip-bot2 for Zheng Zucheng
2024-09-02 1:56 ` [Question] Include isolated cpu to ensure that tasks are not scheduled to isolated cpu？ zhengzucheng
2024-09-02 3:00 ` Waiman Long
2024-09-13 4:03 ` [Question] sched：the load is unbalanced in the VM overcommitment scenario zhengzucheng
2024-09-13 15:55 ` Vincent Guittot
2024-09-14 7:03 ` zhengzucheng
2024-09-17 6:19 ` Vincent Guittot
2024-09-13 17:17 ` Waiman Long
2024-09-14 2:15 ` zhengzucheng
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