Hi Paul,
> In my experience, dcbz slows down the hot-cache case because it adds a > few cycles to the execution time of the inner loop, and on most 64-bit > PowerPC implementations, it doesn't actually help even in the > cold-cache case because the store queue does enough write combining I agree with you that on POWER the dcbz is probably not helping. On PowerPC my experience is different. >From what I have seen DCBZ help enormously on 970,PA-Semi and CELL. Cheers Gunnar Paul Mackerras <[EMAIL PROTECTED] > To Gunnar von 24/06/2008 01:49 Boehn/Germany/Contr/[EMAIL PROTECTED] cc [EMAIL PROTECTED], Mark Nelson <[EMAIL PROTECTED]>, linuxppc-dev@ozlabs.org, Michael Ellerman <[EMAIL PROTECTED]>, [EMAIL PROTECTED], Arnd Bergmann <[EMAIL PROTECTED]> Subject Re: [RFC 1/3] powerpc: __copy_tofrom_user tweaked for Cell Gunnar von Boehn writes: > Interesting points. > Can you help me to understand where the negative effect of DCBZ does come > from? In my experience, dcbz slows down the hot-cache case because it adds a few cycles to the execution time of the inner loop, and on most 64-bit PowerPC implementations, it doesn't actually help even in the cold-cache case because the store queue does enough write combining that the cache doesn't end up reading the line from memory. I don't know whether the Cell PPE can do that, but I could believe that it can't. Paul. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev