linux-kernel - Re: [PATCH 2/3] x86/flush_tlb: try flush_tlb_single one by one in flush_tlb

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Date:	Wed, 2 May 2012 15:44:41 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	Borislav Petkov <bp@...64.org>, andi.kleen@...el.com,
	tim.c.chen@...ux.intel.com, jeremy@...p.org, chrisw@...s-sol.org,
	akataria@...are.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, rostedt@...dmis.org, fweisbec@...il.com,
	riel@...hat.com, luto@....edu, avi@...hat.com, len.brown@...el.com,
	paul.gortmaker@...driver.com, dhowells@...hat.com,
	fenghua.yu@...el.com, yinghai@...nel.org, cpw@....com,
	steiner@....com, linux-kernel@...r.kernel.org,
	yongjie.ren@...el.com
Subject: Re: [PATCH 2/3] x86/flush_tlb: try flush_tlb_single one by one in
 flush_tlb_range

On Wed, May 02, 2012 at 07:38:47PM +0800, Alex Shi wrote:
> > Are you saying you want to have this setting per family?
> 
> Set it according to CPU type is more precise, but looks ugly.

By "CPU type" do you mean microarchitecture here?

> I am wondering if it worth to do. Maybe conservative selection is
> acceptable?

Well, as I said earlier, I'd run it on a couple of different machines
and make FLUSHALL_BAR configurable from userspace - this way you have
real, solid data instead of guessing the exact number.

> > Also, have you run your patches with other benchmarks beside your
> > microbenchmark, say kernbench, SPEC<something>, i.e. some other
> > multithreaded benchmark touching shared memory? Are you seeing any
> > improvement there?
> 
> I tested oltp reading and specjbb2005 with openjdk. They should not much
> flush_tlb_range calling. So, no clear improvement.
> Do you know benchmarks which cause enough flush_tlb_range?

Not really. Probably get a couple of benchmarks and count
flush_tlb_range calls with trace_printk or perf probe? :-)

[..]

> Believe we didn't need to know this, much more thread number just
> weaken and cover the improvement. When the thread number goes down,
> the performance gain appears. So, don't need care this.

Ok, this is also what the data showed, much higher gain with smaller
thread counts.

> Any more comments for this patchset?

Nope, thanks.

-- 
Regards/Gruss,
Boris.

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