From: Oleg Nesterov <oleg@redhat.com>
To: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Fox <afox@redhat.com>,
Stephen Johnston <sjohnsto@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched/cputime: make scale_stime() more precise
Date: Thu, 18 Jul 2019 16:55:49 +0200 [thread overview]
Message-ID: <20190718145549.GA22902@redhat.com> (raw)
In-Reply-To: <20190718131834.GA22211@redhat.com>
On 07/18, Oleg Nesterov wrote:
>
> + * NOTE! currently the only user is cputime_adjust() and thus
> + *
> + * stime < total && rtime > total
> + *
> + * this means that the end result is always precise and the additional
> + * div64_u64_rem() inside the main loop is called at most once.
Ah, I just noticed that the comment is not 100% correct... in theory we
can drop the precision and even do div64_u64_rem() more than once, but this
can only happen if stime or total = stime + utime is "really" huge, I don't
think this can happen in practice...
We can probably just do
static u64 scale_stime(u64 stime, u64 rtime, u64 total)
{
u64 res = 0, div, rem;
if (ilog2(stime) + ilog2(rtime) > 62) {
div = div64_u64_rem(rtime, total, &rem);
res += div * stime;
rtime = rem;
int shift = ilog2(stime) + ilog2(rtime) - 62;
if (shift > 0) {
rtime >>= shift;
total >>= shitt;
if (!total)
return res;
}
}
return res + div64_u64(stime * rtime, total);
}
but this way the code looks less generic.
Oleg.
next prev parent reply other threads:[~2019-07-18 14:55 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-18 13:18 [PATCH] sched/cputime: make scale_stime() more precise Oleg Nesterov
2019-07-18 13:21 ` Oleg Nesterov
2019-07-18 14:55 ` Oleg Nesterov [this message]
2019-07-19 11:03 ` Peter Zijlstra
2019-07-19 13:47 ` Peter Zijlstra
2019-07-19 14:37 ` Oleg Nesterov
2019-07-22 19:56 ` Peter Zijlstra
2019-07-23 14:00 ` Oleg Nesterov
2019-07-23 14:29 ` Oleg Nesterov
2019-07-19 14:03 ` Oleg Nesterov
2019-07-22 19:45 ` Peter Zijlstra
2019-07-22 10:52 ` Stanislaw Gruszka
2019-07-22 20:00 ` Peter Zijlstra
2019-07-23 9:37 ` Stanislaw Gruszka
2020-01-22 16:46 ` Oleg Nesterov
2020-01-23 13:05 ` Oleg Nesterov
2020-01-24 15:42 ` Oleg Nesterov
2020-01-27 12:28 ` [PATCH v2] " Oleg Nesterov
2020-05-15 17:24 ` Oleg Nesterov
2020-05-19 17:25 ` Peter Zijlstra
2020-05-19 18:33 ` Linus Torvalds
2020-05-19 18:42 ` Peter Zijlstra
2020-05-19 19:11 ` Peter Zijlstra
2020-05-19 19:51 ` Linus Torvalds
2020-05-20 15:24 ` Oleg Nesterov
2020-05-20 15:36 ` Peter Zijlstra
2020-05-20 20:10 ` Peter Zijlstra
2020-05-21 13:26 ` Oleg Nesterov
2020-06-16 12:21 ` [tip: sched/core] sched/cputime: Improve cputime_adjust() tip-bot2 for Oleg Nesterov
-- strict thread matches above, loose matches on Subject: below --
2019-07-18 13:15 [PATCH] sched/cputime: make scale_stime() more precise Oleg Nesterov
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