From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: kernel test robot <oliver.sang@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
Peter Zijlstra <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
lkp@lists.01.org, kernel test robot <lkp@intel.com>,
"Huang, Ying" <ying.huang@intel.com>,
Feng Tang <feng.tang@intel.com>,
zhengjun.xing@intel.com
Subject: Re: [x86] d55564cfc2: will-it-scale.per_thread_ops -5.8% regression
Date: Thu, 7 Jan 2021 18:33:58 +0000 [thread overview]
Message-ID: <20210107183358.GG3579531@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAHk-=wgQ5EEH3-GTK9KDB5mBmWjP25YHXC6_-V_KfWd0UTDTDQ@mail.gmail.com>
On Thu, Jan 07, 2021 at 09:43:54AM -0800, Linus Torvalds wrote:
> Before, it would do the whole CLAC/STAC dance inside that loop for
> every entry (and with that commit d55564cfc22 it would be a function
> call, of course).
>
> Can you verify that this fixes the regression (and in fact I'd expect
> it to improve that test-case)?
I'm not sure it's the best approach, TBH. How about simply
for (walk = head; walk; ufds += walk->len, walk = walk->next) {
if (copy_to_user(ufds, walk->entries,
walk->len * sizeof(struct pollfd))
goto out_fds;
}
in there? It's both simpler (obviously matches the copyin side) and
might very well be faster...
next prev parent reply other threads:[~2021-01-07 18:35 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-07 13:47 [x86] d55564cfc2: will-it-scale.per_thread_ops -5.8% regression kernel test robot
2021-01-07 17:43 ` Linus Torvalds
2021-01-07 18:33 ` Al Viro [this message]
2021-01-07 18:40 ` Al Viro
2021-01-07 18:55 ` Al Viro
2021-01-07 18:47 ` Linus Torvalds
2021-01-07 18:58 ` Al Viro
2021-01-07 19:04 ` Al Viro
2021-01-07 19:33 ` Linus Torvalds
2021-01-07 19:57 ` Al Viro
2021-01-08 9:29 ` David Laight
2021-01-08 9:37 ` David Laight
2021-01-08 9:51 ` Peter Zijlstra
2021-01-08 10:44 ` David Laight
2021-01-08 9:49 ` David Laight
2021-01-08 6:13 ` Oliver Sang
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