From: Jan Beulich <jbeulich@suse.com>
To: Julien Grall <julien@xen.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Ian Jackson <iwj@xenproject.org>, Wei Liu <wl@xen.org>,
Stefano Stabellini <sstabellini@kernel.org>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v3 1/5] evtchn: drop acquiring of per-channel lock from send_guest_{global,vcpu}_virq()
Date: Thu, 3 Dec 2020 10:46:34 +0100 [thread overview]
Message-ID: <c15b1e7e-ed9c-b597-2fc1-b8cf89999c55@suse.com> (raw)
In-Reply-To: <70170293-a9a7-282a-dde6-7ed73fc2da48@xen.org>
On 02.12.2020 20:03, Julien Grall wrote:
> On 23/11/2020 13:28, Jan Beulich wrote:
>> The per-vCPU virq_lock, which is being held anyway, together with there
>> not being any call to evtchn_port_set_pending() when v->virq_to_evtchn[]
>> is zero, provide sufficient guarantees.
>
> I agree that the per-vCPU virq_lock is going to be sufficient, however
> dropping the lock also means the event channel locking is more complex
> to understand (the long comment that was added proves it).
>
> In fact, the locking in the event channel code was already proven to be
> quite fragile, therefore I think this patch is not worth the risk.
I agree this is a very reasonable position to take. I probably
would even have remained silent if in the meantime the
spin_lock()s there hadn't changed to read_trylock()s. I really
think we want to limit this unusual locking model to where we
strictly need it. And this change eliminates 50% of them, with
the added benefit of making the paths more lightweight.
Jan
next prev parent reply other threads:[~2020-12-03 9:46 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-23 13:26 [PATCH v3 0/5] evtchn: (not so) recent XSAs follow-on Jan Beulich
2020-11-23 13:28 ` [PATCH v3 1/5] evtchn: drop acquiring of per-channel lock from send_guest_{global,vcpu}_virq() Jan Beulich
2020-12-02 19:03 ` Julien Grall
2020-12-03 9:46 ` Jan Beulich [this message]
2020-12-09 9:53 ` Julien Grall
2020-12-09 14:24 ` Jan Beulich
2020-11-23 13:28 ` [PATCH v3 2/5] evtchn: avoid access tearing for ->virq_to_evtchn[] accesses Jan Beulich
2020-12-02 21:14 ` Julien Grall
2020-11-23 13:28 ` [PATCH v3 3/5] evtchn: convert vIRQ lock to an r/w one Jan Beulich
2020-12-09 11:16 ` Julien Grall
2020-11-23 13:29 ` [PATCH v3 4/5] evtchn: convert domain event " Jan Beulich
2020-12-09 11:54 ` Julien Grall
2020-12-11 10:32 ` Jan Beulich
2020-12-11 10:57 ` Julien Grall
2020-12-14 9:40 ` Jan Beulich
2020-12-21 17:45 ` Julien Grall
2020-12-22 9:46 ` Jan Beulich
2020-12-23 11:22 ` Julien Grall
2020-12-23 12:57 ` Jan Beulich
2020-12-23 13:19 ` Julien Grall
2020-12-23 13:36 ` Jan Beulich
2020-11-23 13:30 ` [PATCH v3 5/5] evtchn: don't call Xen consumer callback with per-channel lock held Jan Beulich
2020-11-30 10:39 ` Isaila Alexandru
2020-12-02 21:10 ` Julien Grall
2020-12-03 10:09 ` Jan Beulich
2020-12-03 14:40 ` Tamas K Lengyel
2020-12-04 11:28 ` Julien Grall
2020-12-04 11:48 ` Jan Beulich
2020-12-04 11:51 ` Julien Grall
2020-12-04 12:01 ` Jan Beulich
2020-12-04 15:09 ` Julien Grall
2020-12-07 8:02 ` Jan Beulich
2020-12-07 17:22 ` Julien Grall
2020-12-04 15:21 ` Tamas K Lengyel
2020-12-04 15:29 ` Julien Grall
2020-12-04 19:15 ` Tamas K Lengyel
2020-12-04 19:22 ` Julien Grall
2020-12-04 21:23 ` Tamas K Lengyel
2020-12-07 15:28 ` Jan Beulich
2020-12-07 17:30 ` Julien Grall
2020-12-07 17:35 ` Tamas K Lengyel
2020-12-23 13:12 ` Jan Beulich
2020-12-23 13:33 ` Julien Grall
2020-12-23 13:41 ` Jan Beulich
2020-12-23 14:44 ` Julien Grall
2020-12-23 14:56 ` Jan Beulich
2020-12-23 15:08 ` Julien Grall
2020-12-23 15:15 ` Tamas K Lengyel
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=c15b1e7e-ed9c-b597-2fc1-b8cf89999c55@suse.com \
--to=jbeulich@suse.com \
--cc=George.Dunlap@eu.citrix.com \
--cc=andrew.cooper3@citrix.com \
--cc=iwj@xenproject.org \
--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).