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 19:04:45 +0000 [thread overview]
Message-ID: <20210107190445.GK3579531@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAHk-=wiZaFRt9hGen9=eOr7LA+Q8o5f980eGEvtxBD6+os7nqA@mail.gmail.com>
On Thu, Jan 07, 2021 at 10:47:07AM -0800, Linus Torvalds wrote:
> Now, the "whole entry" is just 8 bytes, so it's possible that it would
> actually be faster to do a copy of the whole thing rather than write
> just the 16 bits. But I got very nervous about it, because I could
> easily see some threaded app actually changing the 'fd' (or the
> 'event' field) in place (ie writing -1 to it as they close and re-use
> it)
BTW, changing 'event' field in place from another thread is going to
be interesting - you have two 16bit values next to each other and
two CPUs modifying those with no exclusion. Sounds like a recipe
for massive trouble...
Or am I missing something here?
next prev parent reply other threads:[~2021-01-07 19:05 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
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 [this message]
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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