From: Peter Zijlstra <peterz@infradead.org>
To: Josh Don <joshdon@google.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Clement Courbet <courbet@google.com>,
Oleg Rombakh <olegrom@google.com>,
Nick Desaulniers <ndesaulniers@google.com>,
linux-toolchains@vger.kernel.org
Subject: Re: [PATCH] sched: Optimize __calc_delta.
Date: Wed, 3 Mar 2021 11:02:29 +0100 [thread overview]
Message-ID: <YD9etVMPW5A22jxo@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CABk29Ntt88BfqGz=Rjd5Mwyj+N0YLv0Z9QsZp8DgB-n+FV1Zgw@mail.gmail.com>
On Tue, Mar 02, 2021 at 12:57:37PM -0800, Josh Don wrote:
> On gcc, the asm versions of `fls` are about the same speed as the
> builtin. On clang, the versions that use fls (fls,fls64) are more than
> twice as slow as the builtin. This is because the way the `fls` function
> is written, clang puts the value in memory:
> https://godbolt.org/z/EfMbYe. This can be fixed in a separate patch.
Is this because clang gets the asm constraints wrong? ISTR that
happening before, surely the right thing is to fix clang?
next parent reply other threads:[~2021-03-04 0:49 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20210226195239.3905966-1-joshdon@google.com>
[not found] ` <YDliCOPy9s1RdLwd@hirez.programming.kicks-ass.net>
[not found] ` <CABk29Nv7iJEcDg3rgSvfTkXEM69ZeLByJAsZYuA5qpdj645nZw@mail.gmail.com>
[not found] ` <CABk29Ntt88BfqGz=Rjd5Mwyj+N0YLv0Z9QsZp8DgB-n+FV1Zgw@mail.gmail.com>
2021-03-03 10:02 ` Peter Zijlstra [this message]
2021-03-03 22:00 ` [PATCH] sched: Optimize __calc_delta Josh Don
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