From: Davidlohr Bueso <dave@stgolabs.net>
To: Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] locking/rwsem: Make owner store task pointer of last owning reader
Date: Mon, 10 Sep 2018 10:15:50 -0700 [thread overview]
Message-ID: <20180910171550.GA3902@linux-r8p5> (raw)
In-Reply-To: <83b333ea-8ef2-84ea-6810-4ab1a67eef88@redhat.com>
On Mon, 10 Sep 2018, Waiman Long wrote:
>One major issue with a combined count/owner is that we may have to use
>cmpxchg for reader lock which will certainly impact reader-heavy
>workloads. I have also thought about ways to compress the task pointer
>address so that it can use fewer bits and leave the rests for reader
>count. It is probably doable on 64-bit systems, but likely not on 32-bit
>system given that there are less bits to play around.
Yeah we've discussed this before. As a cleanup it would obviously be good,
but I fear about raw performance loss when using cmpxchg instead of xadd.
Thanks,
Davidlohr
next prev parent reply other threads:[~2018-09-10 17:16 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 20:18 [PATCH] locking/rwsem: Make owner store task pointer of last owning reader Waiman Long
2018-09-10 9:31 ` Peter Zijlstra
2018-09-10 15:01 ` Waiman Long
2018-09-10 17:15 ` Davidlohr Bueso [this message]
2018-09-10 17:35 ` Waiman Long
2018-09-11 8:17 ` Peter Zijlstra
2018-09-11 12:56 ` Waiman Long
2018-09-11 19:21 ` Davidlohr Bueso
2018-09-11 19:38 ` Peter Zijlstra
2018-09-10 10:54 ` [tip:locking/core] " tip-bot for Waiman Long
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180910171550.GA3902@linux-r8p5 \
--to=dave@stgolabs.net \
--cc=linux-kernel@vger.kernel.org \
--cc=longman@redhat.com \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.