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From: Julien Grall <julien@xen.org>
To: Jan Beulich <jbeulich@suse.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.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>,
	"Roger Pau Monné" <roger.pau@citrix.com>,
	"Kevin Tian" <kevin.tian@intel.com>
Subject: Re: [PATCH v5 2/6] evtchn: convert domain event lock to an r/w one
Date: Thu, 7 Jul 2022 19:00:26 +0100	[thread overview]
Message-ID: <6683c78f-ab19-ebe7-b6f9-32019f2226ef@xen.org> (raw)
In-Reply-To: <5f5fc6a7-6e27-8275-0f05-11ba5454156a@suse.com>

Hi Jan,

As discussed in [1], I think it would good to revive this patch.

AFAICT, this patch was dropped because the performance was thought to be 
minimal. However, I think it would be a better way to resolve the 
problem that one is trying to address [1].

So I will do another review of this patch.

On 27/01/2021 08:16, Jan Beulich wrote:
> Especially for the use in evtchn_move_pirqs() (called when moving a vCPU
> across pCPU-s) and the ones in EOI handling in PCI pass-through code,
> serializing perhaps an entire domain isn't helpful when no state (which
> isn't e.g. further protected by the per-channel lock) changes.
> Unfortunately this implies dropping of lock profiling for this lock,
> until r/w locks may get enabled for such functionality.
> While ->notify_vcpu_id is now meant to be consistently updated with the
> per-channel lock held, an extension applies to ECS_PIRQ: The field is
> also guaranteed to not change with the per-domain event lock held for
> writing. Therefore the link_pirq_port() call from evtchn_bind_pirq()
> could in principle be moved out of the per-channel locked regions, but
> this further code churn didn't seem worth it.

This doesn't seem to apply on upstream anymore. Would you be able to 
respin it?

I have looked at the place where you use read_lock() rather than 
write_lock(). They all look fine to me, so I would be fine to give my 
reviewed-by on the next version (assuming there are nothing wrong with 
the rebase :)).



Julien Grall

  parent reply	other threads:[~2022-07-07 18:01 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-27  8:13 [PATCH v5 0/6] evtchn: (not so) recent XSAs follow-on Jan Beulich
2021-01-27  8:15 ` [PATCH v5 1/6] evtchn: use per-channel lock where possible Jan Beulich
2021-01-27  8:16 ` [PATCH v5 2/6] evtchn: convert domain event lock to an r/w one Jan Beulich
2021-05-27 11:01   ` Roger Pau Monné
2021-05-27 11:16     ` Jan Beulich
2022-07-07 18:00   ` Julien Grall [this message]
2021-01-27  8:16 ` [PATCH v5 3/6] evtchn: slightly defer lock acquire where possible Jan Beulich
2021-01-27  8:16 ` [PATCH v5 4/6] evtchn: add helper for port_is_valid() + evtchn_from_port() Jan Beulich
2021-01-27  8:17 ` [PATCH v5 5/6] evtchn: type adjustments Jan Beulich
2021-01-27  8:17 ` [PATCH v5 6/6] evtchn: drop acquiring of per-channel lock from send_guest_{global,vcpu}_virq() Jan Beulich
2021-04-21 15:23 ` Ping: [PATCH v5 0/6] evtchn: (not so) recent XSAs follow-on Jan Beulich
2021-04-21 15:56   ` Julien Grall
2021-04-22  8:53     ` Jan Beulich
2021-05-14 15:29       ` Roger Pau Monné
2021-05-17  7:15         ` Jan Beulich

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