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From: Roman Bolshakov <r.bolshakov@yadro.com>
To: Alexander Graf <agraf@csgraf.de>
Cc: Peter Maydell <peter.maydell@linaro.org>,
	Eduardo Habkost <ehabkost@redhat.com>,
	Richard Henderson <richard.henderson@linaro.org>,
	qemu-devel <qemu-devel@nongnu.org>,
	Cameron Esfahani <dirty@apple.com>,
	qemu-arm <qemu-arm@nongnu.org>,
	Claudio Fontana <cfontana@suse.de>, Frank Yang <lfy@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Peter Collingbourne <pcc@google.com>
Subject: Re: [PATCH 2/8] hvf: Move common code out
Date: Fri, 4 Dec 2020 02:04:07 +0300	[thread overview]
Message-ID: <20201203230407.GB14685@SPB-NB-133.local> (raw)
In-Reply-To: <2a286418-aa8e-17b9-1be2-58b0b361dec5@csgraf.de>

On Thu, Dec 03, 2020 at 11:13:35PM +0100, Alexander Graf wrote:
> 
> On 03.12.20 19:42, Peter Collingbourne wrote:
> > On Thu, Dec 3, 2020 at 1:41 AM Roman Bolshakov <r.bolshakov@yadro.com> wrote:
> > > On Mon, Nov 30, 2020 at 04:00:11PM -0800, Peter Collingbourne wrote:
> > > > What I observe is that when returning from a pending signal pselect
> > > > consumes the signal (which is also consistent with my understanding of
> > > > what pselect does). That means that it doesn't matter if we take a
> > > > second WFx exit because once we reach the pselect in the second WFx
> > > > exit the signal will have been consumed by the pselect in the first
> > > > exit and we will just wait for the next one.
> > > > 
> > > Aha! Thanks for the explanation. So, the first WFI in the series of
> > > guest WFIs will likely wake up immediately? After a period without WFIs
> > > there must be a pending SIG_IPI...
> > > 
> > > It shouldn't be a critical issue though because (as defined in D1.16.2)
> > > "the architecture permits a PE to leave the low-power state for any
> > > reason, it is permissible for a PE to treat WFI as a NOP, but this is
> > > not recommended for lowest power operation."
> > > 
> > > BTW. I think a bit from the thread should go into the description of
> > > patch 8, because it's not trivial and it would really be helpful to keep
> > > in repo history. At least something like this (taken from an earlier
> > > reply in the thread):
> > > 
> > >    In this implementation IPI is blocked on the CPU thread at startup and
> > >    pselect() is used to atomically unblock the signal and begin sleeping.
> > >    The signal is sent unconditionally so there's no need to worry about
> > >    races between actually sleeping and the "we think we're sleeping"
> > >    state. It may lead to an extra wakeup but that's better than missing
> > >    it entirely.
> > Okay, I'll add something like that to the next version of the patch I send out.
> 
> 
> If this is the only change, I've already added it for v4. If you want me to
> change it further, just let me know what to replace the patch description
> with.
> 
> 

Thanks, Alex.

I'm fine with the description and all set.

-Roman


  reply	other threads:[~2020-12-03 23:06 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-26 21:50 [PATCH 0/8] hvf: Implement Apple Silicon Support Alexander Graf
2020-11-26 21:50 ` [PATCH 1/8] hvf: Add hypervisor entitlement to output binaries Alexander Graf
2020-11-27  4:54   ` Paolo Bonzini
2020-11-27 19:44   ` Roman Bolshakov
2020-11-27 21:17     ` Paolo Bonzini
2020-11-27 21:51     ` Alexander Graf
2020-11-26 21:50 ` [PATCH 2/8] hvf: Move common code out Alexander Graf
2020-11-27 20:00   ` Roman Bolshakov
2020-11-27 21:55     ` Alexander Graf
2020-11-27 23:30       ` Frank Yang
2020-11-30 20:15         ` Frank Yang
2020-11-30 20:33           ` Alexander Graf
2020-11-30 20:55             ` Frank Yang
2020-11-30 21:08               ` Peter Collingbourne
2020-11-30 21:40                 ` Alexander Graf
2020-11-30 23:01                   ` Peter Collingbourne
2020-11-30 23:18                     ` Alexander Graf
2020-12-01  0:00                       ` Peter Collingbourne
2020-12-01  0:13                         ` Alexander Graf
2020-12-01  8:21                           ` [PATCH] arm/hvf: Optimize and simplify WFI handling Peter Collingbourne via
2020-12-01 11:16                             ` Alexander Graf
2020-12-01 18:59                               ` Peter Collingbourne
2020-12-01 22:03                                 ` Alexander Graf
2020-12-02  1:19                                   ` Peter Collingbourne
2020-12-02  1:53                                     ` Alexander Graf
2020-12-02  4:44                                       ` Peter Collingbourne
2020-12-03 10:12                                 ` Roman Bolshakov
2020-12-03 18:30                                   ` Peter Collingbourne
2020-12-01 16:26                             ` Alexander Graf
2020-12-01 20:03                               ` Peter Collingbourne
2020-12-01 22:09                                 ` Alexander Graf
2020-12-01 23:13                                   ` Alexander Graf
2020-12-02  0:52                                   ` Peter Collingbourne
2020-12-03  9:41                         ` [PATCH 2/8] hvf: Move common code out Roman Bolshakov
2020-12-03 18:42                           ` Peter Collingbourne
2020-12-03 22:13                             ` Alexander Graf
2020-12-03 23:04                               ` Roman Bolshakov [this message]
2020-12-01  0:37                   ` Roman Bolshakov
2020-11-30 22:10               ` Peter Maydell
2020-12-01  2:49                 ` Frank Yang
2020-11-30 22:46               ` Peter Collingbourne
2020-11-26 21:50 ` [PATCH 3/8] arm: Set PSCI to 0.2 for HVF Alexander Graf
2020-11-26 21:50 ` [PATCH 4/8] arm: Synchronize CPU on PSCI on Alexander Graf
2020-11-26 21:50 ` [PATCH 5/8] hvf: Add Apple Silicon support Alexander Graf
2020-11-26 21:50 ` [PATCH 6/8] hvf: Use OS provided vcpu kick function Alexander Graf
2020-11-26 22:18   ` Eduardo Habkost
2020-11-30  2:42     ` Alexander Graf
2020-11-30  7:45       ` Claudio Fontana
2020-11-26 21:50 ` [PATCH 7/8] arm: Add Hypervisor.framework build target Alexander Graf
2020-11-27  4:59   ` Paolo Bonzini
2020-11-26 21:50 ` [PATCH 8/8] hw/arm/virt: Disable highmem when on hypervisor.framework Alexander Graf
2020-11-26 22:14   ` Eduardo Habkost
2020-11-26 22:29     ` Peter Maydell
2020-11-27 16:26       ` Eduardo Habkost
2020-11-27 16:38         ` Peter Maydell
2020-11-27 16:47           ` Eduardo Habkost
2020-11-27 16:53             ` Peter Maydell
2020-11-27 17:17               ` Eduardo Habkost
2020-11-27 18:16                 ` Peter Maydell
2020-11-27 18:20                   ` Eduardo Habkost
2020-11-27 16:47           ` Peter Maydell
2020-11-30  2:40             ` Alexander Graf
2020-11-26 22:10 ` [PATCH 0/8] hvf: Implement Apple Silicon Support Eduardo Habkost
2020-11-27 17:48   ` Philippe Mathieu-Daudé

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