linux-kernel - Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's

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Date:	Mon, 21 Oct 2013 10:31:38 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	sebastien.dugue@...l.net, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's

On Sun, 2013-10-20 at 17:29 -0400, Neil Horman wrote:
> On Fri, Oct 18, 2013 at 02:15:52PM -0700, Eric Dumazet wrote:
> > On Fri, 2013-10-18 at 16:11 -0400, Neil Horman wrote:
> > 
> > > #define BUFSIZ_ORDER 4
> > > #define BUFSIZ ((2 << BUFSIZ_ORDER) * (1024*1024*2))
> > > static int __init csum_init_module(void)
> > > {
> > > 	int i;
> > > 	__wsum sum = 0;
> > > 	struct timespec start, end;
> > > 	u64 time;
> > > 	struct page *page;
> > > 	u32 offset = 0;
> > > 
> > > 	page = alloc_pages((GFP_TRANSHUGE & ~__GFP_MOVABLE), BUFSIZ_ORDER);
> > 
> > Not sure what you are doing here, but its not correct.
> > 
> Why not?  You asked for a test with 32 hugepages, so I allocated 32 hugepages.

Not really. We cannot allocate 64 Mbytes in a single alloc_pages() call
on x86. (MAX_ORDER = 11)

You noticed nothing because you did not 
write anything on the 64Mbytes area (and corrupt memory) or
use CONFIG_DEBUG_PAGEALLOC=y.

Your code read data out of bounds and was lucky, thats all...

You in fact allocated a page of (4096<<4) bytes



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