Re: [PATCH]: Fix SMP-reordering race in mark_buffer_dirty

[Linus Torvalds]

On Thu, 3 Apr 2008, Mikulas Patocka wrote:
> 
> When I added memory reads around mfence, the combined result was worse 
> than the sum of reads and mfence --- mfence alone 8 ticks, mfence+4reads 
> 18 ticks.

Sorry, my test-program was buggy.

> mfence+writes scales linearly, i.e. mfence + 4 writes does 12 ticks.

I get different results now that I fixed my memop test. I get a loop with 
reads and writes taking 3 cycles without mfence, and 21 cycles with (read 
after, write before). 

			Linus
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