On Thu, Sep 14, 2006 at 05:03:08PM -0700, Andrew Morton wrote: > On Thu, 14 Sep 2006 16:36:12 -0700 > Badari Pulavarty <pbadari@xxxxxxxxxx> wrote: > > > Hi Andrew, > > > > I have been working on tracking down ~20% performance degrade for > > sequential read performance for ext3. > > oop. I'd kinda prefer that we discover things like this before the patch > gets into mainline. > > > Finally narrowed it down to get_blocks() support. If I force > > ext3_get_blocks_handle() to always return 1 block - I get better > > IO rate. I did all the usual stuff, tracked down requests, traced > > blocksizes, looked at readahead code, looked at mpage_readpages() > > etc.. I still can't figure out how to explain the degrade.. > > > > Any suggestions on how to track it down. > > Learn to driver Jens's blktrace stuff, find out why the IO scheduling went > bad. > > Number one suspicion: the buffer_boundary() stuff isn't working. I think you are right about that - perhaps something along the lines of the following patch (untested) would help ? If this is the problem then I guess the degradation should show up for DIO as well. ----------------------------- The boundary block check in ext3_get_blocks_handle needs to be adjusted against the count of blocks mapped in this call, now that it can map more than one block. linux-2.6.18-rc5-suparna/fs/ext3/inode.c | 2 +- 1 files changed, 1 insertion(+), 1 deletion(-) diff -puN fs/ext3/inode.c~ext3-multiblock-boundary-fix fs/ext3/inode.c --- linux-2.6.18-rc5/fs/ext3/inode.c~ext3-multiblock-boundary-fix 2006-09-15 10:53:12.000000000 +0530 +++ linux-2.6.18-rc5-suparna/fs/ext3/inode.c 2006-09-15 10:54:30.000000000 +0530 @@ -925,7 +925,7 @@ int ext3_get_blocks_handle(handle_t *han set_buffer_new(bh_result); got_it: map_bh(bh_result, inode->i_sb, le32_to_cpu(chain[depth-1].key)); - if (blocks_to_boundary == 0) + if (count > blocks_to_boundary) set_buffer_boundary(bh_result); err = count; /* Clean up and exit */ _ Regards Suparna -- Suparna Bhattacharya (suparna@xxxxxxxxxx) Linux Technology Center IBM Software Lab, India - 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
