linux-kernel - Re: [PATCH 1/3] sched/wait: use freezable

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Message-ID: <20190202183743.GA229953@google.com>
Date:   Sat, 2 Feb 2019 13:37:43 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Hugo Lefeuvre <hle@....eu.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Greg Hartman <ghartman@...gle.com>,
        Alistair Strachan <strachan@...gle.com>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Christian Brauner <christian@...uner.io>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] sched/wait: use freezable_schedule when possible

On Fri, Feb 01, 2019 at 06:38:05AM +0100, Hugo Lefeuvre wrote:
> Replace schedule(); try_to_freeze() by freezable_schedule().
> 
> Tasks calling freezable_schedule() set the PF_FREEZER_SKIP flag
> before calling schedule(). Unlike tasks calling schedule();
> try_to_freeze() tasks calling freezable_schedule() are not awaken by
> try_to_freeze_tasks(). Instead they call try_to_freeze() when they
> wake up if the freeze is still underway.
> 
> It is not a problem since sleeping tasks can't do anything which isn't
> allowed for a frozen task while sleeping.
> 
> The result is a potential performance gain during freeze, since less
> tasks have to be awaken.

I'm curious did you try the freezing process and see if pointless wakeups are
reduced?  That would be an added bonus if you did.

Otherwise seems like a nice change. Peter and Rafael, what do you think?

thanks,

 - Joel