[PATCH] jbd: fix transaction batching (fe1dcbc4) · Commits · 戴 / test

Ben points out that: When writing files out using O_SYNC, jbd's 1 jiffy delay results in a significant drop in throughput as the disk sits idle. The patch below results in a 4-5x performance improvement (from 6.5MB/s to ~24-30MB/s on my IDE test box) when writing out files using O_SYNC. So optimise the batching code by omitting it entirely if the process which is doing a sync write is the same as the one which did the most recent sync write. If that's true, we're unlikely to get any other processes joining the transaction. (Has been in -mm for ages - it took me a long time to get on to performance testing it) Numbers, on write-cache-disabled IDE: /usr/bin/time -p synctest -n 10 -uf -t 1 -p 1 dir-name Unpatched: 40 seconds Patched: 35 seconds Batching disabled: 35 seconds This is the problematic single-process-doing-fsync case. With multiple fsyncing processes the numbers are AFACIT unaltered by the patch. Aside: performance testing and instrumentation shows that the transaction batching almost doesn't help (testing with synctest -n 1 -uf -t 100 -p 10 dir-name on non-writeback-caching IDE). This is because by the time one process is running a synchronous commit, a bunch of other processes already have a transaction handle open, so they're all going to batch into the same transaction anyway. The batching seems to offer maybe 5-10% speedup with this workload, but I'm pretty sure it was more important than that when it was first developed 4-odd years ago... Cc: "Stephen C. Tweedie" <sct@redhat.com> Cc: Benjamin LaHaise <bcrl@kvack.org> Signed-off-by:

Andrew Morton <akpm@osdl.org> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

fs/jbd/transaction.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -1308,6 +1308,7 @@ int journal_stop(handle_t *handle)
		transaction_t *transaction = handle->h_transaction;
		journal_t *journal = transaction->t_journal;
		int old_handle_count, err;
		pid_t pid;

		J_ASSERT(transaction->t_updates > 0);
		J_ASSERT(journal_current_handle() == handle);
		@@ -1333,8 +1334,15 @@ int journal_stop(handle_t *handle)
		* It doesn't cost much - we're about to run a commit and sleep
		* on IO anyway. Speeds up many-threaded, many-dir operations
		* by 30x or more...
		*
		* But don't do this if this process was the most recent one to
		* perform a synchronous write. We do this to detect the case where a
		* single process is doing a stream of sync writes. No point in waiting
		* for joiners in that case.
		*/
		if (handle->h_sync) {
		pid = current->pid;
		if (handle->h_sync && journal->j_last_sync_writer != pid) {
		journal->j_last_sync_writer = pid;
		do {
		old_handle_count = transaction->t_handle_count;
		schedule_timeout_uninterruptible(1);

include/linux/jbd.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -23,6 +23,7 @@
		#define jfs_debug jbd_debug
		#else

		#include <linux/types.h>
		#include <linux/buffer_head.h>
		#include <linux/journal-head.h>
		#include <linux/stddef.h>
		@@ -618,6 +619,7 @@ struct transaction_s
		* @j_wbuf: array of buffer_heads for journal_commit_transaction
		* @j_wbufsize: maximum number of buffer_heads allowed in j_wbuf, the
		* number that will fit in j_blocksize
		* @j_last_sync_writer: most recent pid which did a synchronous write
		* @j_private: An opaque pointer to fs-private information.
		*/

		@@ -807,6 +809,8 @@ struct journal_s
		struct buffer_head **j_wbuf;
		int j_wbufsize;

		pid_t j_last_sync_writer;

		/*
		* An opaque pointer to fs-private information. ext3 puts its
		* superblock pointer here

Admin message