From: Jan Beulich <jbeulich@suse.com>
To: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Julien Grall <julien@xen.org>, Wei Liu <wl@xen.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>,
George Dunlap <george.dunlap@citrix.com>,
xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [PATCH v7 2/5] xen/rcu: don't use stop_machine_run() for rcu_barrier()
Date: Wed, 25 Mar 2020 14:19:49 +0100 [thread overview]
Message-ID: <51626ddf-7f59-73a6-f0df-300a39482b9f@suse.com> (raw)
In-Reply-To: <20200325105511.20882-3-jgross@suse.com>
On 25.03.2020 11:55, Juergen Gross wrote:
> Today rcu_barrier() is calling stop_machine_run() to synchronize all
> physical cpus in order to ensure all pending rcu calls have finished
> when returning.
>
> As stop_machine_run() is using tasklets this requires scheduling of
> idle vcpus on all cpus imposing the need to call rcu_barrier() on idle
> cpus only in case of core scheduling being active, as otherwise a
> scheduling deadlock would occur.
>
> There is no need at all to do the syncing of the cpus in tasklets, as
> rcu activity is started in __do_softirq() called whenever softirq
> activity is allowed. So rcu_barrier() can easily be modified to use
> softirq for synchronization of the cpus no longer requiring any
> scheduling activity.
>
> As there already is a rcu softirq reuse that for the synchronization.
>
> Remove the barrier element from struct rcu_data as it isn't used.
>
> Finally switch rcu_barrier() to return void as it now can never fail.
>
> Partially-based-on-patch-by: Igor Druzhinin <igor.druzhinin@citrix.com>
> Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
next prev parent reply other threads:[~2020-03-25 13:20 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-25 10:55 [Xen-devel] [PATCH v7 0/5] xen/rcu: let rcu work better with core scheduling Juergen Gross
2020-03-25 10:55 ` [Xen-devel] [PATCH v7 1/5] xen: introduce smp_mb__[after|before]_atomic() barriers Juergen Gross
2020-03-25 13:17 ` Jan Beulich
2020-03-25 16:20 ` Julien Grall
2020-03-25 10:55 ` [Xen-devel] [PATCH v7 2/5] xen/rcu: don't use stop_machine_run() for rcu_barrier() Juergen Gross
2020-03-25 13:19 ` Jan Beulich [this message]
2020-03-25 16:13 ` Julien Grall
2020-03-26 6:58 ` Jan Beulich
2020-03-26 7:24 ` Jürgen Groß
2020-03-26 8:49 ` Jan Beulich
2020-03-26 8:50 ` Jürgen Groß
2020-03-26 9:14 ` Julien Grall
2020-03-25 10:55 ` [Xen-devel] [PATCH v7 3/5] xen: don't process rcu callbacks when holding a rcu_read_lock() Juergen Gross
2020-03-25 10:55 ` [Xen-devel] [PATCH v7 4/5] xen/rcu: add assertions to debug build Juergen Gross
2020-03-25 10:55 ` [Xen-devel] [PATCH v7 5/5] xen/rcu: add per-lock counter in debug builds Juergen Gross
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=51626ddf-7f59-73a6-f0df-300a39482b9f@suse.com \
--to=jbeulich@suse.com \
--cc=andrew.cooper3@citrix.com \
--cc=george.dunlap@citrix.com \
--cc=ian.jackson@eu.citrix.com \
--cc=jgross@suse.com \
--cc=julien@xen.org \
--cc=sstabellini@kernel.org \
--cc=wl@xen.org \
--cc=xen-devel@lists.xenproject.org \
/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).