From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>, James Morse <james.morse@arm.com>
Cc: Zhenzhong Duan <zhenzhong.duan@oracle.com>,
LKML <linux-kernel@vger.kernel.org>,
SRINIVAS <srinivas.eeda@oracle.com>,
Borislav Petkov <bp@alien8.de>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: Question about qspinlock nest
Date: Fri, 18 Jan 2019 09:50:12 -0500 [thread overview]
Message-ID: <abf2dfe7-e148-b011-764d-b9effa573d5d@redhat.com> (raw)
In-Reply-To: <20190118100229.GB27931@hirez.programming.kicks-ass.net>
On 01/18/2019 05:02 AM, Peter Zijlstra wrote:
>
>> e.g. We can't take an SError during the SError handler.
>>
>> But we can take this SError/NMI on another CPU while the first one is still
>> running the handler.
>>
>> These multiple NMIlike notifications mean having multiple locks/fixmap-slots,
>> one per notification. This is where the qspinlock node limit comes in, as we
>> could have more than 4 contexts.
> Right; so Waiman was going to do a patch that reverts to test-and-set or
> something along those lines once we hit the queue limit, which seems
> like a good way out. Actually hitting that nesting level should be
> exceedingly rare.
Yes, I am working on a patch to support arbitrary levels of nesting. It
is easy for PV qspinlock as lock stealing is supported.
For native qspinlock, we cannot do lock stealing without incurring a
certain amount of overhead in the regular slowpath code. It was up to
10% in my own testing. So I am exploring an alternative that can do the
job without incurring any noticeable performance degradation in the
slowpath. I ran into a race condition which I am still trying to find
out where that comes from. Hopefully, I will have something to post next
week.
Cheers,
Longman
next prev parent reply other threads:[~2019-01-18 14:50 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-10 8:02 Question about qspinlock nest Zhenzhong Duan
2019-01-10 14:43 ` Waiman Long
2019-01-10 18:25 ` James Morse
2019-01-10 19:23 ` Waiman Long
2019-01-10 20:12 ` Peter Zijlstra
2019-01-11 18:32 ` James Morse
2019-01-14 13:16 ` Peter Zijlstra
2019-01-14 13:54 ` James Morse
2019-01-14 21:07 ` Waiman Long
2019-01-18 10:02 ` Peter Zijlstra
2019-01-18 10:24 ` Borislav Petkov
2019-01-18 14:50 ` Waiman Long [this message]
2019-01-18 20:06 ` Peter Zijlstra
2019-01-18 21:30 ` Waiman Long
[not found] ` <2eca6f60-3e8b-a389-27cb-8adbd9676607@oracle.com>
2019-01-11 9:16 ` Peter Zijlstra
2019-01-11 17:36 ` Borislav Petkov
2019-01-11 16:59 ` Waiman Long
2019-01-10 20:03 ` Peter Zijlstra
2019-01-14 9:25 Zhenzhong Duan
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=abf2dfe7-e148-b011-764d-b9effa573d5d@redhat.com \
--to=longman@redhat.com \
--cc=bp@alien8.de \
--cc=james.morse@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=srinivas.eeda@oracle.com \
--cc=zhenzhong.duan@oracle.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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).