On 21/04/2020 17:04, William Tu wrote:
On Tue, Apr 21, 2020 at 09:23:57AM +0100, [email protected] wrote:
From: Anton Ivanov <[email protected]>
We do not check metadata - mtime, atime, anywhere, so we
do not need to update it every time we sync the log.
if the system supports it, the log update should be
data only
Signed-off-by: Anton Ivanov <[email protected]>
LGTM,
But how do you know we do not check mtime or atime of the ovsdb log file?
By searching through the code :)
stat and stat64 are fairly easy to grep for and so is their use. They are
mostly confined to ssl-stream.c
If there isn't a lot of performance overhead updating the metadata,
why not keep it as it is now?
The performance overhead on a spinning rust disk is massive - it is several
times. In fact, you can hear it. My source trees are on a SAS 7.2K RPM array
and with the current upstream the testsuite sounds like a hectic Call of Duty
bout.
With this, the sound becomes much "smoother" - you can hear that the disks are
no longer searching like crazy.
On a non-rotational - not so much, but still in the 10s of percent. The kernel
has to issue at least two sets of requests instead of one and there is quite a
bit of locking and barriers on metadata updates.
A.
William
---
ovsdb/log.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/ovsdb/log.c b/ovsdb/log.c
index c82a79c9f..41af77679 100644
--- a/ovsdb/log.c
+++ b/ovsdb/log.c
@@ -658,7 +658,16 @@ ovsdb_log_write_and_free(struct ovsdb_log *log, struct
json *json)
struct ovsdb_error *
ovsdb_log_commit_block(struct ovsdb_log *file)
{
+#if (_POSIX_C_SOURCE >= 199309L || _XOPEN_SOURCE >= 500)
+ /* we do not check metadata - mtime, atime, anywhere, so we
+ * do not need to update it every time we sync the log.
+ * if the system supports it, the log update should be
+ * data only
+ */
+ if (file->stream && fdatasync(fileno(file->stream))) {
+#else
if (file->stream && fsync(fileno(file->stream))) {
+#endif
return ovsdb_io_error(errno, "%s: fsync failed", file->display_name);
}
return NULL;
--
2.20.1
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--
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/
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