On Mon 08-06-15 12:47:26, Ted Tso wrote: > On Thu, Apr 02, 2015 at 03:58:19PM +0200, Jan Kara wrote: > > jbd2_journal_get_write_access() and jbd2_journal_get_create_access() are > > frequently called for buffers that are already part of the running > > transaction - most frequently it is the case for bitmaps, inode table > > blocks, and superblock. Since in such cases we have nothing to do, it is > > unfortunate we still grab reference to journal head, lock the bh, lock > > bh_state only to find out there's nothing to do. > > > > Improving this is a bit subtle though since until we find out journal > > head is attached to the running transaction, it can disappear from under > > us because checkpointing / commit decided it's no longer needed. We deal > > with this by protecting journal_head slab with RCU. We still have to be > > careful about journal head being freed & reallocated within slab and > > about exposing journal head in consistent state (in particular > > b_modified and b_frozen_data must be in correct state before we allow > > user to touch the buffer). > > > > FIXME: Performance data. > > > > Signed-off-by: Jan Kara <jack@xxxxxxx> > > Applied, so we can start getting some testing on this patch. Did you > ever get performance data? Yes. Here are results for reaim fserver workload for 32 core machine with 128 GB of ram with ext4 on ramdisk: Procs Vanilla Patched 1 20420.688 21155.556 21 49684.704 178934.074 41 84630.364 196647.482 61 106344.284 204831.652 81 120751.370 214842.428 101 131585.450 208761.832 121 138092.078 212741.648 141 142271.578 212118.502 161 146008.364 213731.388 181 149569.494 216121.444 Numbers are operations per second so larger is better. You can see that for 21 processes we get increase by 260% in the number operations. Also the total maximum of operations the machine is able to achieve increases by 44% because of overall lower CPU overhead. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
