From: Marcelo Tosatti <mtosatti@redhat.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.com>,
Leonardo Bras <leobras.c@gmail.com>,
linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
linux-mm@kvack.org, Johannes Weiner <hannes@cmpxchg.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Shakeel Butt <shakeel.butt@linux.dev>,
Muchun Song <muchun.song@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Vlastimil Babka <vbabka@suse.cz>,
Hyeonggon Yoo <42.hyeyoo@gmail.com>,
Leonardo Bras <leobras@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Waiman Long <longman@redhat.com>,
Boqun Feng <boqun.feng@gmail.com>,
Frederic Weisbecker <fweisbecker@suse.de>
Subject: Re: [PATCH 0/4] Introduce QPW for per-cpu operations
Date: Mon, 23 Feb 2026 08:20:51 -0300 [thread overview]
Message-ID: <aZw4E9+aN3QjMZsB@tpad> (raw)
In-Reply-To: <aZwZrw_LTilXsPd4@tiehlicka>
On Mon, Feb 23, 2026 at 10:11:11AM +0100, Michal Hocko wrote:
> On Fri 20-02-26 16:01:59, Marcelo Tosatti wrote:
> > On Fri, Feb 20, 2026 at 06:58:10PM +0100, Vlastimil Babka wrote:
> [...]
> > > >> So if we can assume that workloads on isolated cpus make syscalls only
> > > >> rarely, and when they do they can tolerate them being slower, I think the
> > > >> "avoid sheaves on isolated cpus" would be the best way here.
> > > >
> > > > I am not sure its safe to assume that. Ask Gemini about isolcpus use
> > > > cases and:
> > >
> > > I don't think it's answering the question about syscalls. But didn't read
> > > too closely given the nature of it.
> >
> > People use isolcpus with all kinds of programs.
> >
> > > > For example, AF_XDP bypass uses system calls (and wants isolcpus):
> > > >
> > > > https://www.quantvps.com/blog/kernel-bypass-in-hft?srsltid=AfmBOoryeSxuuZjzTJIC9O-Ag8x4gSwjs-V4Xukm2wQpGmwDJ6t4szuE
> > >
> > > Didn't spot system calls mentioned TBH.
> >
> > I don't see why you want to reduce performance of applications that
> > execute on isolcpus=, if you can avoid that.
>
> If you can avoid that by making performance bad for everybody else then
> then it seems safer to sacrifice those workloads that are much more
> special - i.e. cpu isolation.
> --
> Michal Hocko
> SUSE Labs
Performance is not bad for everyone else:
Without patchset:
================
[ 1188.050725] kmalloc_bench: Avg cycles per kmalloc: 159
With qpw patchset, CONFIG_QPW=n:
================================
[ 50.292190] kmalloc_bench: Avg cycles per kmalloc: 163
And its probably possible to remove those 4 cycles.
Which makes reduction of performance of isolcpus not necessary.
next prev parent reply other threads:[~2026-02-24 18:26 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-06 14:34 Marcelo Tosatti
2026-02-06 14:34 ` [PATCH 1/4] Introducing qpw_lock() and per-cpu queue & flush work Marcelo Tosatti
2026-02-06 15:20 ` Marcelo Tosatti
2026-02-07 0:16 ` Leonardo Bras
2026-02-11 12:09 ` Marcelo Tosatti
2026-02-14 21:32 ` Leonardo Bras
2026-02-06 14:34 ` [PATCH 2/4] mm/swap: move bh draining into a separate workqueue Marcelo Tosatti
2026-02-06 14:34 ` [PATCH 3/4] swap: apply new queue_percpu_work_on() interface Marcelo Tosatti
2026-02-07 1:06 ` Leonardo Bras
2026-02-06 14:34 ` [PATCH 4/4] slub: " Marcelo Tosatti
2026-02-07 1:27 ` Leonardo Bras
2026-02-06 23:56 ` [PATCH 0/4] Introduce QPW for per-cpu operations Leonardo Bras
2026-02-10 14:01 ` Michal Hocko
2026-02-11 12:01 ` Marcelo Tosatti
2026-02-11 12:11 ` Marcelo Tosatti
2026-02-14 21:35 ` Leonardo Bras
2026-02-11 16:38 ` Michal Hocko
2026-02-11 16:50 ` Marcelo Tosatti
2026-02-11 16:59 ` Vlastimil Babka
2026-02-11 17:07 ` Michal Hocko
2026-02-14 22:02 ` Leonardo Bras
2026-02-16 11:00 ` Michal Hocko
2026-02-19 15:27 ` Marcelo Tosatti
2026-02-19 19:30 ` Michal Hocko
2026-02-20 14:30 ` Marcelo Tosatti
2026-02-23 9:18 ` Michal Hocko
2026-02-23 21:56 ` Frederic Weisbecker
2026-02-24 17:23 ` Marcelo Tosatti
2026-02-20 10:48 ` Vlastimil Babka
2026-02-20 12:31 ` Michal Hocko
2026-02-20 17:35 ` Marcelo Tosatti
2026-02-20 17:58 ` Vlastimil Babka
2026-02-20 19:01 ` Marcelo Tosatti
2026-02-23 9:11 ` Michal Hocko
2026-02-23 11:20 ` Marcelo Tosatti [this message]
2026-02-24 14:40 ` Frederic Weisbecker
2026-02-24 18:12 ` Marcelo Tosatti
2026-02-20 16:51 ` Marcelo Tosatti
2026-02-20 16:55 ` Marcelo Tosatti
2026-02-20 22:38 ` Leonardo Bras
2026-02-23 18:09 ` Vlastimil Babka
2026-02-20 21:58 ` Leonardo Bras
2026-02-23 9:06 ` Michal Hocko
2026-02-19 13:15 ` Marcelo Tosatti
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=aZw4E9+aN3QjMZsB@tpad \
--to=mtosatti@redhat.com \
--cc=42.hyeyoo@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=boqun.feng@gmail.com \
--cc=cgroups@vger.kernel.org \
--cc=cl@linux.com \
--cc=fweisbecker@suse.de \
--cc=hannes@cmpxchg.org \
--cc=iamjoonsoo.kim@lge.com \
--cc=leobras.c@gmail.com \
--cc=leobras@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=longman@redhat.com \
--cc=mhocko@suse.com \
--cc=muchun.song@linux.dev \
--cc=penberg@kernel.org \
--cc=rientjes@google.com \
--cc=roman.gushchin@linux.dev \
--cc=shakeel.butt@linux.dev \
--cc=tglx@linutronix.de \
--cc=vbabka@suse.com \
--cc=vbabka@suse.cz \
/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