linux-kernel - Re: [RFC][PATCH] dm: Remove dm_bufio_cond

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Date:   Thu, 22 Sep 2016 22:59:30 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mikulas Patocka <mpatocka@...hat.com>
cc:     Peter Zijlstra <peterz@...radead.org>,
        Mike Snitzer <snitzer@...hat.com>,
        Alasdair Kergon <agk@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        dm-devel@...hat.com, Joe Thornber <ejt@...hat.com>
Subject: Re: [RFC][PATCH] dm: Remove dm_bufio_cond_resched()

On Thu, 22 Sep 2016, Mikulas Patocka wrote:
> On Mon, 19 Sep 2016, Peter Zijlstra wrote:
> 
> > On Tue, Sep 13, 2016 at 09:39:59AM -0400, Mike Snitzer wrote:
> > > So I'm not sure how this dm-bufio local cond_resched() wrapper still got
> > > in... happy to take your patch.
> > > 
> > > Please respond with whatever SOB you'd like applied to the patch header.
> > 
> > Sorry, for the delay, here goes.
> 
> Why not change it to might_sleep()? - that would be almost equivalent to 

You mean might_resched(). might_sleep() is not even remotely equivalent.

> If we call the cond_resched() function in tight loops such as walking all 
> buffers in a list, there may be performance penalty due to the call, so 
> the call should be done only if it is really needed (i.e. in 
> CONFIG_PREEMPT_VOLUNTARY case).

Makes sense.

Thanks,

	tglx