linux-kernel - Re: [PATCH v4 5/7] x86/tlb: add tlb flush all factor for specific CPU

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Message-ID: <1336727058.2527.144.camel@twins>
Date:	Fri, 11 May 2012 11:04:18 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Alex Shi <alex.shi@...el.com>
Cc:	rob@...dley.net, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, arnd@...db.de, rostedt@...dmis.org,
	fweisbec@...il.com, jeremy@...p.org, gregkh@...uxfoundation.org,
	borislav.petkov@....com, riel@...hat.com, luto@....edu,
	avi@...hat.com, len.brown@...el.com, dhowells@...hat.com,
	fenghua.yu@...el.com, ak@...ux.intel.com, cpw@....com,
	steiner@....com, akpm@...ux-foundation.org, penberg@...nel.org,
	hughd@...gle.com, rientjes@...gle.com,
	kosaki.motohiro@...fujitsu.com, n-horiguchi@...jp.nec.com,
	paul.gortmaker@...driver.com, trenn@...e.de, tj@...nel.org,
	oleg@...hat.com, axboe@...nel.dk, kamezawa.hiroyu@...fujitsu.com,
	viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/7] x86/tlb: add tlb flush all factor for specific
 CPU

On Fri, 2012-05-11 at 08:49 +0800, Alex Shi wrote:
> On 05/10/2012 05:38 PM, Peter Zijlstra wrote:
> 
> > On Thu, 2012-05-10 at 13:00 +0800, Alex Shi wrote:
> > 
> > 
> >> +void intel_tlb_flushall_factor_set(struct cpuinfo_x86 *c)
> >> +{
> >> +       if (!cpu_has_invlpg) {
> >> +               tlb_flushall_factor = -1;
> >> +               return;
> >> +       }
> > 
> > ...
> > 
> >> +       if (!cpu_has_invlpg || vma->vm_flags & VM_HUGETLB
> >> +                       || tlb_flushall_factor == (u16)TLB_FLUSH_ALL)
> >> {
> >>  flush_all: 
> > 
> > Since you set tlb_flushall_factor (I'd have called it _shift) to -1
> > when !invlpg there's a redundant check in there.
> > 
> 
> 
> 
> NO, the first judgement is from CPU. But second '-1' is may from user
> setting in sysfs.

Then you're doing it wrong. Don't allow setting the sysfs variable if !
cpu_has_invlpg.
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