linux-kernel - Re: [PATCH 0 of 9] x86/smp function calls: convert x86 tlb flushes to use function calls [POST 2]

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Date:	Mon, 18 Aug 2008 22:37:29 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	Andi Kleen <andi@...stfloor.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH 0 of 9] x86/smp function calls: convert x86 tlb flushes
 to use function calls [POST 2]

Ingo Molnar wrote:
> nice stuff!
>
> I suspect the extra cost might be worth it for two reasons: 1) we could 
> optimize the cross-call implementation further

Unfortunately, I think the kmalloc fix for the RCU issue is going to
hurt quite a lot.

>  2) on systems where TLB 
> flushes actually matter, the ability to overlap multiple TLB flushes to 
> the same single CPU might improve workloads.
>   

...perhaps.

> FYI, i've created a new -tip topic for your patches, tip/x86/tlbflush. 
> It's based on tip/irq/sparseirq (there are a good deal of dependencies 
> with that topic).
>   

Really?  I didn't see much conflict when rebasing onto current tip.git. 
Just an incidental context conflict in entry_arch.h.

> It would be nice to see some numbers on sufficiently SMP systems, using 
> some mmap/munmap intense workload.

I've attached my test program: tlb-mash.c.  Compile with "gcc -o
tlb-mash tlb-mash.c -lpthread" and run with ./tlb-mash X, where X is the
number of threads to run (2x cpus works well).  It keeps running until
killed, with each thread repeatedly mprotecting a page within a shared
mapping.

    J

View attachment "tlb-mash.c" of type "text/x-csrc" (1211 bytes)