linux-kernel - Re: [PATCH 2/2] block: Convert BDI proportion calculations to flexible proportions

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Message-ID: <20120529125452.GB23991@quack.suse.cz>
Date:	Tue, 29 May 2012 14:54:52 +0200
From:	Jan Kara <jack@...e.cz>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, Sasha Levin <levinsasha928@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] block: Convert BDI proportion calculations to
 flexible proportions

On Tue 29-05-12 14:38:31, Peter Zijlstra wrote:
> On Tue, 2012-05-29 at 14:34 +0200, Jan Kara wrote:
> 
> > The only safe solution seems to be to create a variant of percpu counters
> > that can be used from an interrupt. Or do you have other idea Peter?
> 
> > > [   20.680186]  [<ffffffff8325ac9b>] _raw_spin_lock+0x3b/0x70
> > > [   20.680186]  [<ffffffff81993527>] ? __percpu_counter_sum+0x17/0xc0
> > > [   20.680186]  [<ffffffff81993527>] __percpu_counter_sum+0x17/0xc0
> > > [   20.680186]  [<ffffffff810ebf90>] ? init_timer_deferrable_key+0x20/0x20
> > > [   20.680186]  [<ffffffff8195b5c2>] fprop_new_period+0x12/0x60
> > > [   20.680186]  [<ffffffff811d929d>] writeout_period+0x3d/0xa0
> > > [   20.680186]  [<ffffffff810ec0bf>] call_timer_fn+0x12f/0x260
> > > [   20.680186]  [<ffffffff810ebf90>] ? init_timer_deferrable_key+0x20/0x20
> 
> Yeah, just make sure IRQs are disabled around doing that ;-)
  Evil ;) But we'd need to have IRQs disabled also in each
fprop_fraction_percpu() call, and generally, if we want things clean, we'd
need to disable them in all entry points to proportion code (or at least
around all percpu calls)...

								Honza
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