From: Peter Zijlstra <peterz@infradead.org>
To: Yu Zhe <yuzhe@nfschina.com>
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org,
liqiong@nfschina.com
Subject: Re: [PATCH] x86/aperfmperf: use time_is_before_jiffies(a + b) to replace "jiffies - a > b"
Date: Wed, 27 Jul 2022 18:00:34 +0200 [thread overview]
Message-ID: <YuFhIgsUgNJ+o9xG@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20220727031405.26892-1-yuzhe@nfschina.com>
On Wed, Jul 27, 2022 at 11:14:05AM +0800, Yu Zhe wrote:
> time_is_before_jiffies deals with timer wrapping correctly.
Please explain how the current code does not.
>
> Signed-off-by: Yu Zhe <yuzhe@nfschina.com>
> ---
> arch/x86/kernel/cpu/aperfmperf.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
> index 1f60a2b27936..22e0bac3fffe 100644
> --- a/arch/x86/kernel/cpu/aperfmperf.c
> +++ b/arch/x86/kernel/cpu/aperfmperf.c
> @@ -423,7 +423,7 @@ unsigned int arch_freq_get_on_cpu(int cpu)
> * Bail on invalid count and when the last update was too long ago,
> * which covers idle and NOHZ full CPUs.
> */
> - if (!mcnt || (jiffies - last) > MAX_SAMPLE_AGE)
> + if (!mcnt || time_is_before_jiffies(last + MAX_SAMPLE_AGE))
> goto fallback;
>
> return div64_u64((cpu_khz * acnt), mcnt);
> --
> 2.11.0
>
next prev parent reply other threads:[~2022-07-27 16:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-27 3:14 Yu Zhe
2022-07-27 16:00 ` Peter Zijlstra [this message]
2022-07-28 2:55 ` Yu Zhe
2022-07-28 10:30 ` Peter Zijlstra
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