From: Peter Zijlstra <peterz@infradead.org>
To: Giovanni Gherdovich <ggherdovich@suse.cz>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@suse.de>,
Len Brown <lenb@kernel.org>,
"Rafael J . Wysocki" <rjw@rjwysocki.net>,
x86@kernel.org, linux-pm@vger.kernel.org,
linux-kernel@vger.kernel.org,
Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 2/2] x86, sched: Bail out of frequency invariance if turbo frequency is unknown
Date: Fri, 1 May 2020 15:04:27 +0200 [thread overview]
Message-ID: <20200501130427.GD3762@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200428132450.24901-3-ggherdovich@suse.cz>
On Tue, Apr 28, 2020 at 03:24:50PM +0200, Giovanni Gherdovich wrote:
> There may be CPUs that support turbo boost but don't declare any turbo
> ratio, i.e. their MSR_TURBO_RATIO_LIMIT is all zeroes. In that condition
> scale-invariant calculations can't be performed.
>
> Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
> Suggested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance")
> ---
> arch/x86/kernel/smpboot.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 4718f29a3065..ab2a0df7d1fb 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1991,9 +1991,11 @@ static bool intel_set_max_freq_ratio(void)
> /*
> * Some hypervisors advertise X86_FEATURE_APERFMPERF
> * but then fill all MSR's with zeroes.
> + * Some CPUs have turbo boost but don't declare any turbo ratio
> + * in MSR_TURBO_RATIO_LIMIT.
> */
> - if (!base_freq) {
> - pr_debug("Couldn't determine cpu base frequency, necessary for scale-invariant accounting.\n");
> + if (!base_freq || !turbo_freq) {
> + pr_debug("Couldn't determine cpu base or turbo frequency, necessary for scale-invariant accounting.\n");
> return false;
> }
I've added the below, imagine base_freq > turbo_freq *
SCHED_CAPACITY_SCALE.
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1975,6 +1975,7 @@ static bool core_set_max_freq_ratio(u64
static bool intel_set_max_freq_ratio(void)
{
u64 base_freq, turbo_freq;
+ u64 turbo_ratio;
if (slv_set_max_freq_ratio(&base_freq, &turbo_freq))
goto out;
@@ -2008,9 +2009,15 @@ static bool intel_set_max_freq_ratio(voi
return false;
}
- arch_turbo_freq_ratio = div_u64(turbo_freq * SCHED_CAPACITY_SCALE,
- base_freq);
+ turbo_ratio = div_u64(turbo_freq * SCHED_CAPACITY_SCALE, base_freq);
+ if (!turbo_ratio) {
+ pr_debug("Non-zero turbo and base frequencies led to a 0 ratio.\n");
+ return false;
+ }
+
+ arch_turbo_freq_ratio = turbo_ratio;
arch_set_max_freq_ratio(turbo_disabled());
+
return true;
}
next prev parent reply other threads:[~2020-05-01 13:05 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-28 13:24 [PATCH 0/2] More frequency invariance fixes for x86 Giovanni Gherdovich
2020-04-28 13:24 ` [PATCH 1/2] x86, sched: Prevent divisions by zero in frequency invariant accounting Giovanni Gherdovich
2020-04-29 11:30 ` Rafael J. Wysocki
2020-05-01 13:30 ` Peter Zijlstra
2020-05-02 14:25 ` Giovanni Gherdovich
2020-05-18 22:20 ` Ricardo Neri
2020-05-19 16:46 ` Giovanni Gherdovich
2020-04-28 13:24 ` [PATCH 2/2] x86, sched: Bail out of frequency invariance if turbo frequency is unknown Giovanni Gherdovich
2020-04-29 11:30 ` Rafael J. Wysocki
2020-05-01 13:04 ` Peter Zijlstra [this message]
2020-05-02 0:06 ` Ricardo Neri
2020-05-02 14:26 ` Giovanni Gherdovich
2020-05-02 0:04 ` Ricardo Neri
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