Messages in this thread | | | Date | Thu, 4 Mar 2004 05:52:12 +0100 | From | Andrea Arcangeli <> | Subject | Re: 2.4.23aa2 (bugfixes and important VM improvements for the high end) |
| |
On Wed, Mar 03, 2004 at 08:07:04PM -0800, Andrew Morton wrote: > That's a larger difference than I expected. But then, everyone has been
mysql is threaded (it's not using processes that force tlb flushes at every context switch), so the only time a tlb flush ever happens is when a syscall or an irq or a page fault happens with 4:4. Not tlb flush would ever happen with 3:1 in the whole workload (yeah, some background tlb flushing happens anyways when you type char on bash or move the mouse of course but it's very low frequency)
(to be fair, because it's threaded it means they also find 512m of address space lost more problematic than the db using processes, though besides the reduced address space there would be no measurable slowdown with 2.5:1.5)
Also the 4:4 pretty much depends on the vgettimeofday to be backported from the x86-64 tree and an userspace to use it, so the test may be repeated with vgettimeofday, though it's very possible mysql isn't using that much gettimeofday as other databases, especially the I/O bound workload shouldn't matter that much with gettimeofday.
another reason could be the xeon bit, all numbers I've seen were on p3, that's why I was asking about xeon and p4 or more recent.
all random ideas, just guessing.
> mysteriously quiet with the 4g/4g benchmarking.
indeed.
> A kernel profile would be interesting. As would an optimisation effort, > which, as far as I know, has never been undertaken.
yes, though I doubt you'll find anything interesting in the kernel, the slowdown should happen because the userspace runs slower, it's like undercloking the cpu, it's not a bottleneck in the kernel that can be optimized (at least unless there are bugs in the patch which I think not). - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |