On (18/01/08 00:19), Martin Knoblauch didst pronounce: > > > The effect is defintely depending on the IO hardware. > > > performed the same tests > > > on a different box with an AACRAID controller and there things > > > look different. > > > > I take it different also means it does not show this odd performance > > behaviour and is similar whether the patch is applied or not? > > > > Here are the numbers (MB/s) from the AACRAID box, after a fresh boot: > > Test 2.6.19.2 2.6.24-rc6 2.6.24-rc6-81eabcbe0b991ddef5216f30ae91c4b226d54b6d > dd1 325 350 290 > dd1-dir 180 160 160 > dd2 2x 90 2x113 2x110 > dd2-dir 2x120 2x 92 2x 93 > dd3 3x 54 3x 70 3x 70 > dd3-dir 3x 83 3x 64 3x 64 > mix3 55,2x 30 400,2x 25 310,2x 25 > > What we are seing here is that: > > a) DIRECT IO takes a much bigger hit (2.6.19 vs. 2.6.24) on this IO system compared to the CCISS box > b) Reverting your patch hurts single stream Right, and this is consistent with other complaints about the PFN of the page mattering to some hardware. > c) dual/triple stream are not affected by your patch and are improved over 2.6.19 I am not very surprised. The callers to the page allocator are probably making no special effort to get a batch of pages in PFN-order. They are just assuming that subsequent calls give contiguous pages. With two or more threads involved, there will not be a correlation between physical pages and what is on disk any more. > d) the mix3 performance is improved compared to 2.6.19. > d1) reverting your patch hurts the local-disk part of mix3 > e) the AACRAID setup is definitely faster than the CCISS. > > So, on this box your patch is definitely needed to get the pre-2.6.24 performance > when writing a single big file. > > Actually things on the CCISS box might be even more complicated. I forgot the fact > that on that box we have ext2/LVM/DM/Hardware, while on the AACRAID box we have > ext2/Hardware. Do you think that the LVM/MD are sensitive to the page order/coloring? > I don't have enough experience with LVM setups to make an intelligent guess. > Anyway: does your patch only address this performance issue, or are there also > data integrity concerns without it? Performance issue only. There are no data integrity concerns with that patch. > I may consider reverting the patch for my > production environment. It really helps two thirds of my boxes big time, while it does > not hurt the other third that much :-) > That is certainly an option. > > > > > > I can certainly stress the box before doing the tests. Please > > > define "many" for the kernel compiles :-) > > > > > > > With 8GiB of RAM, try making 24 copies of the kernel and compiling them > > all simultaneously. Running that for for 20-30 minutes should be enough > > > to randomise the freelists affecting what color of page is used for the > > dd test. > > > > ouch :-) OK, I will try that. > Thanks. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
