* [PATCH 0/2] xfs: small metadata performance optimisations @ 2011-08-08 6:51 Dave Chinner 2011-08-08 6:51 ` [PATCH 1/2] xfs: Don't allocate new buffers on every call to _xfs_buf_find Dave Chinner 2011-08-08 6:51 ` [PATCH 2/2] xfs: reduce the number of log forces from tail pushing Dave Chinner 0 siblings, 2 replies; 6+ messages in thread From: Dave Chinner @ 2011-08-08 6:51 UTC (permalink / raw) To: xfs These are a couple of small optimisations that I made after noticing just how rare buffer cache misses are and where log forces are being triggered from most commonly during highly concurrent metadata workloads. _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs ^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH 1/2] xfs: Don't allocate new buffers on every call to _xfs_buf_find 2011-08-08 6:51 [PATCH 0/2] xfs: small metadata performance optimisations Dave Chinner @ 2011-08-08 6:51 ` Dave Chinner 2011-08-09 7:51 ` Christoph Hellwig 2011-08-08 6:51 ` [PATCH 2/2] xfs: reduce the number of log forces from tail pushing Dave Chinner 1 sibling, 1 reply; 6+ messages in thread From: Dave Chinner @ 2011-08-08 6:51 UTC (permalink / raw) To: xfs From: Dave Chinner <dchinner@redhat.com> Stats show that for an 8-way unlink @ ~80,000 unlinks/s we are doing ~1 million cache hit lookups to ~3000 buffer creates. That's almost 3 orders of magnitude more cahce hits than misses, so optimising for cache hits is quite important. In the cache hit case, we do not need to allocate a new buffer in case of a cache miss, so we are effectively hitting the allocator for no good reason for vast the majority of calls to _xfs_buf_find. 8-way create workloads are showing similar cache hit/miss ratios. The result is profiles that look like this: samples pcnt function DSO _______ _____ _______________________________ _________________ 1036.00 10.0% _xfs_buf_find [kernel.kallsyms] 582.00 5.6% kmem_cache_alloc [kernel.kallsyms] 519.00 5.0% __memcpy [kernel.kallsyms] 468.00 4.5% __ticket_spin_lock [kernel.kallsyms] 388.00 3.7% kmem_cache_free [kernel.kallsyms] 331.00 3.2% xfs_log_commit_cil [kernel.kallsyms] Further, there is a fair bit of work involved in initialising a new buffer once a cache miss has occurred and we currently do that under the rbtree spinlock. That increases spinlock hold time on what are heavily used trees. To fix this, remove the initialisation of the buffer from _xfs_buf_find() and only allocate the new buffer once we've had a cache miss. Initialise the buffer immediately after allocating it in xfs_buf_get, too, so that is it ready for insert if we get another cache miss after allocation. This minimises lock hold time and avoids unnecessary allocator churn. The resulting profiles look like: samples pcnt function DSO _______ _____ ___________________________ _________________ 8111.00 9.1% _xfs_buf_find [kernel.kallsyms] 4380.00 4.9% __memcpy [kernel.kallsyms] 4341.00 4.8% __ticket_spin_lock [kernel.kallsyms] 3401.00 3.8% kmem_cache_alloc [kernel.kallsyms] 2856.00 3.2% xfs_log_commit_cil [kernel.kallsyms] 2625.00 2.9% __kmalloc [kernel.kallsyms] 2380.00 2.7% kfree [kernel.kallsyms] 2016.00 2.3% kmem_cache_free [kernel.kallsyms] Showing a significant reduction in time spent doing allocation and freeing from slabs (kmem_cache_alloc and kmem_cache_free). Signed-off-by: Dave Chinner <dchinner@redhat.com> --- fs/xfs/linux-2.6/xfs_buf.c | 34 ++++++++++++++++++++-------------- 1 files changed, 20 insertions(+), 14 deletions(-) diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c index c57836d..56c685c 100644 --- a/fs/xfs/linux-2.6/xfs_buf.c +++ b/fs/xfs/linux-2.6/xfs_buf.c @@ -481,8 +481,6 @@ _xfs_buf_find( /* No match found */ if (new_bp) { - _xfs_buf_initialize(new_bp, btp, range_base, - range_length, flags); rb_link_node(&new_bp->b_rbnode, parent, rbp); rb_insert_color(&new_bp->b_rbnode, &pag->pag_buf_tree); /* the buffer keeps the perag reference until it is freed */ @@ -529,30 +527,38 @@ found: * Storage in memory for all portions of the buffer will be allocated, * although backing storage may not be. */ -xfs_buf_t * +struct xfs_buf * xfs_buf_get( - xfs_buftarg_t *target,/* target for buffer */ + struct xfs_buftarg *target,/* target for buffer */ xfs_off_t ioff, /* starting offset of range */ size_t isize, /* length of range */ xfs_buf_flags_t flags) { - xfs_buf_t *bp, *new_bp; + struct xfs_buf *bp; + struct xfs_buf *new_bp = NULL; int error = 0; - new_bp = xfs_buf_allocate(flags); - if (unlikely(!new_bp)) - return NULL; - +again: bp = _xfs_buf_find(target, ioff, isize, flags, new_bp); - if (bp == new_bp) { + if (!(bp || new_bp)) { + new_bp = xfs_buf_allocate(flags); + if (unlikely(!new_bp)) + return NULL; + + _xfs_buf_initialize(new_bp, target, ioff << BBSHIFT, + isize << BBSHIFT, flags); + goto again; + } + + if (!bp) { + xfs_buf_deallocate(new_bp); + return NULL; + } else if (bp == new_bp) { error = xfs_buf_allocate_memory(bp, flags); if (error) goto no_buffer; - } else { + } else if (new_bp) xfs_buf_deallocate(new_bp); - if (unlikely(bp == NULL)) - return NULL; - } if (!(bp->b_flags & XBF_MAPPED)) { error = _xfs_buf_map_pages(bp, flags); -- 1.7.5.4 _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH 1/2] xfs: Don't allocate new buffers on every call to _xfs_buf_find 2011-08-08 6:51 ` [PATCH 1/2] xfs: Don't allocate new buffers on every call to _xfs_buf_find Dave Chinner @ 2011-08-09 7:51 ` Christoph Hellwig 2011-08-10 5:48 ` Dave Chinner 0 siblings, 1 reply; 6+ messages in thread From: Christoph Hellwig @ 2011-08-09 7:51 UTC (permalink / raw) To: Dave Chinner; +Cc: xfs On Mon, Aug 08, 2011 at 04:51:10PM +1000, Dave Chinner wrote: > -xfs_buf_t * > +struct xfs_buf * > xfs_buf_get( > - xfs_buftarg_t *target,/* target for buffer */ > + struct xfs_buftarg *target,/* target for buffer */ > xfs_off_t ioff, /* starting offset of range */ > size_t isize, /* length of range */ > xfs_buf_flags_t flags) > { > - xfs_buf_t *bp, *new_bp; > + struct xfs_buf *bp; > + struct xfs_buf *new_bp = NULL; > int error = 0; > > - new_bp = xfs_buf_allocate(flags); > - if (unlikely(!new_bp)) > - return NULL; > - > +again: > bp = _xfs_buf_find(target, ioff, isize, flags, new_bp); > - if (bp == new_bp) { > + if (!(bp || new_bp)) { > + new_bp = xfs_buf_allocate(flags); > + if (unlikely(!new_bp)) > + return NULL; > + > + _xfs_buf_initialize(new_bp, target, ioff << BBSHIFT, > + isize << BBSHIFT, flags); > + goto again; > + } > + > + if (!bp) { > + xfs_buf_deallocate(new_bp); > + return NULL; > + } else if (bp == new_bp) { > error = xfs_buf_allocate_memory(bp, flags); > if (error) > goto no_buffer; > - } else { > + } else if (new_bp) > xfs_buf_deallocate(new_bp); > - if (unlikely(bp == NULL)) > - return NULL; > - } The while loop looks a bit confusing to me. Why not unroll it similar to how it's done for the VFS inode cache: bp = _xfs_buf_find(target, ioff, isize, flags, new_bp); if (bp) goto found; new_bp = xfs_buf_allocate(flags); if (unlikely(!new_bp)) return NULL; _xfs_buf_initialize(new_bp, target, ioff << BBSHIFT, isize << BBSHIFT, flags); bp = _xfs_buf_find(target, ioff, isize, flags, new_bp); if (!bp) { xfs_buf_deallocate(new_bp); return NULL; } if (bp == new_bp) { error = xfs_buf_allocate_memory(bp, flags); if (error) goto no_buffer; } found: or even better make sure all buffer initialization is done either as part of xfs_buf_find or the caller - although we'd need a variant with caller locking if we want to go down the latter route. This variant would be nessecary if we ever want to add shared/exclusive or RCU locking for buffer lookup anyway. There's also some other weird things here that should be cleaned up when touching it: - we should never be able to find a buffer with the wrong mapped state, so this could be replaced by an assert - there should be no need to re-assign b_bn and b_count_desired when we find a buffer _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 1/2] xfs: Don't allocate new buffers on every call to _xfs_buf_find 2011-08-09 7:51 ` Christoph Hellwig @ 2011-08-10 5:48 ` Dave Chinner 0 siblings, 0 replies; 6+ messages in thread From: Dave Chinner @ 2011-08-10 5:48 UTC (permalink / raw) To: Christoph Hellwig; +Cc: xfs On Tue, Aug 09, 2011 at 03:51:51AM -0400, Christoph Hellwig wrote: > On Mon, Aug 08, 2011 at 04:51:10PM +1000, Dave Chinner wrote: > > -xfs_buf_t * > > +struct xfs_buf * > > xfs_buf_get( > > - xfs_buftarg_t *target,/* target for buffer */ > > + struct xfs_buftarg *target,/* target for buffer */ > > xfs_off_t ioff, /* starting offset of range */ > > size_t isize, /* length of range */ > > xfs_buf_flags_t flags) > > { > > - xfs_buf_t *bp, *new_bp; > > + struct xfs_buf *bp; > > + struct xfs_buf *new_bp = NULL; > > int error = 0; > > > > - new_bp = xfs_buf_allocate(flags); > > - if (unlikely(!new_bp)) > > - return NULL; > > - > > +again: > > bp = _xfs_buf_find(target, ioff, isize, flags, new_bp); > > - if (bp == new_bp) { > > + if (!(bp || new_bp)) { > > + new_bp = xfs_buf_allocate(flags); > > + if (unlikely(!new_bp)) > > + return NULL; > > + > > + _xfs_buf_initialize(new_bp, target, ioff << BBSHIFT, > > + isize << BBSHIFT, flags); > > + goto again; > > + } > > + > > + if (!bp) { > > + xfs_buf_deallocate(new_bp); > > + return NULL; > > + } else if (bp == new_bp) { > > error = xfs_buf_allocate_memory(bp, flags); > > if (error) > > goto no_buffer; > > - } else { > > + } else if (new_bp) > > xfs_buf_deallocate(new_bp); > > - if (unlikely(bp == NULL)) > > - return NULL; > > - } > > The while loop looks a bit confusing to me. Why not unroll it similar > to how it's done for the VFS inode cache: > > bp = _xfs_buf_find(target, ioff, isize, flags, new_bp); > if (bp) > goto found; > > new_bp = xfs_buf_allocate(flags); > if (unlikely(!new_bp)) > return NULL; > _xfs_buf_initialize(new_bp, target, ioff << BBSHIFT, isize << BBSHIFT, > flags); > bp = _xfs_buf_find(target, ioff, isize, flags, new_bp); > if (!bp) { > xfs_buf_deallocate(new_bp); > return NULL; > } > > if (bp == new_bp) { > error = xfs_buf_allocate_memory(bp, flags); > if (error) > goto no_buffer; > } > found: Makes sense. > or even better make sure all buffer initialization is done either as > part of xfs_buf_find or the caller - although we'd need a variant > with caller locking if we want to go down the latter route. This > variant would be nessecary if we ever want to add shared/exclusive or > RCU locking for buffer lookup anyway. I'll leave that problem for when RCU-izing the lookup - I haven't quite worked out what the best way of doing that is yet, anyway. > There's also some other weird things here that should be cleaned up > when touching it: > > - we should never be able to find a buffer with the wrong mapped > state, so this could be replaced by an assert OK. > - there should be no need to re-assign b_bn and b_count_desired > when we find a buffer Yes, definitely. I'm also tempted to rename some variables to make it more obvious what units they are in and to reduce the conversions we do from one type to another. Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs ^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH 2/2] xfs: reduce the number of log forces from tail pushing 2011-08-08 6:51 [PATCH 0/2] xfs: small metadata performance optimisations Dave Chinner 2011-08-08 6:51 ` [PATCH 1/2] xfs: Don't allocate new buffers on every call to _xfs_buf_find Dave Chinner @ 2011-08-08 6:51 ` Dave Chinner 2011-08-14 16:31 ` Christoph Hellwig 1 sibling, 1 reply; 6+ messages in thread From: Dave Chinner @ 2011-08-08 6:51 UTC (permalink / raw) To: xfs From: Dave Chinner <dchinner@redhat.com> The AIL push code will issue a log force on ever single push loop that it exits and has encountered pinned items. It doesn't rescan these pinned items until it revisits the AIL from the start. Hence we only need to force the log once per walk from the start of the AIL to the target LSN. This results in numbers like this: xs_push_ail_flush..... 1456 xs_log_force......... 1485 For an 8-way 50M inode create workload - almost all the log forces are coming from the AIL pushing code. Reduce the number of log forces by only forcing the log if the previous walk found pinned buffers. This reduces the numbers to: xs_push_ail_flush..... 665 xs_log_force......... 682 For the same test. Signed-off-by: Dave Chinner <dchinner@redhat.com> --- fs/xfs/xfs_trans_ail.c | 18 +++++++++++++++++- fs/xfs/xfs_trans_priv.h | 1 + 2 files changed, 18 insertions(+), 1 deletions(-) diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c index c15aa29..7a74bca 100644 --- a/fs/xfs/xfs_trans_ail.c +++ b/fs/xfs/xfs_trans_ail.c @@ -377,6 +377,7 @@ xfs_ail_worker( int count = 0; int push_xfsbufd = 0; +again: spin_lock(&ailp->xa_lock); target = ailp->xa_target; lip = xfs_trans_ail_cursor_first(ailp, &cur, ailp->xa_last_pushed_lsn); @@ -392,6 +393,20 @@ xfs_ail_worker( XFS_STATS_INC(xs_push_ail); /* + * If last time we ran we encountered pinned items, force the log first, + * wait for it and then push again. + */ + if (ailp->xa_last_pushed_lsn == 0 && + ailp->xa_log_flush) { + ailp->xa_log_flush = 0; + xfs_trans_ail_cursor_done(ailp, &cur); + spin_unlock(&ailp->xa_lock); + XFS_STATS_INC(xs_push_ail_flush); + xfs_log_force(mp, SYNC_WAIT); + goto again; + } + + /* * While the item we are looking at is below the given threshold * try to flush it out. We'd like not to stop until we've at least * tried to push on everything in the AIL with an LSN less than @@ -435,7 +450,7 @@ xfs_ail_worker( case XFS_ITEM_PINNED: XFS_STATS_INC(xs_push_ail_pinned); stuck++; - flush_log = 1; + ailp->xa_log_flush++; break; case XFS_ITEM_LOCKED: @@ -500,6 +515,7 @@ out_done: if (!count) { /* We're past our target or empty, so idle */ ailp->xa_last_pushed_lsn = 0; + ailp->xa_log_flush = 0; /* * We clear the XFS_AIL_PUSHING_BIT first before checking diff --git a/fs/xfs/xfs_trans_priv.h b/fs/xfs/xfs_trans_priv.h index 212946b..0a6eec6 100644 --- a/fs/xfs/xfs_trans_priv.h +++ b/fs/xfs/xfs_trans_priv.h @@ -71,6 +71,7 @@ struct xfs_ail { struct delayed_work xa_work; xfs_lsn_t xa_last_pushed_lsn; unsigned long xa_flags; + int xa_log_flush; }; #define XFS_AIL_PUSHING_BIT 0 -- 1.7.5.4 _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH 2/2] xfs: reduce the number of log forces from tail pushing 2011-08-08 6:51 ` [PATCH 2/2] xfs: reduce the number of log forces from tail pushing Dave Chinner @ 2011-08-14 16:31 ` Christoph Hellwig 0 siblings, 0 replies; 6+ messages in thread From: Christoph Hellwig @ 2011-08-14 16:31 UTC (permalink / raw) To: Dave Chinner; +Cc: xfs The flush_log variable in xfs_ail_worker is non-zero after your patch, and can be removed. The second argument for xfs_log_force to force a sync log force is XFS_LOG_SYNC, not SYNC_WAIT. I also don't really like the goto again style - we can just move the log push at the beggining of the function, the only thing it requires is adding an additional list_empty check, e.g.: spin_lock(&ailp->xa_lock); /* * If last time we ran we encountered pinned items, force the log * first, wait for it and then push again. */ if (ailp->xa_last_pushed_lsn == 0 && ailp->xa_log_flush && !list_empty(&ailp->xa_ail)) { ailp->xa_log_flush = 0; spin_unlock(&ailp->xa_lock); XFS_STATS_INC(xs_push_ail_flush); xfs_log_force(mp, SYNC_WAIT); spin_lock(&ailp->xa_lock); } target = ailp->xa_target; lip = xfs_trans_ail_cursor_first(ailp, &cur, ailp->xa_last_pushed_lsn); _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2011-08-14 16:31 UTC | newest] Thread overview: 6+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2011-08-08 6:51 [PATCH 0/2] xfs: small metadata performance optimisations Dave Chinner 2011-08-08 6:51 ` [PATCH 1/2] xfs: Don't allocate new buffers on every call to _xfs_buf_find Dave Chinner 2011-08-09 7:51 ` Christoph Hellwig 2011-08-10 5:48 ` Dave Chinner 2011-08-08 6:51 ` [PATCH 2/2] xfs: reduce the number of log forces from tail pushing Dave Chinner 2011-08-14 16:31 ` Christoph Hellwig
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