George Spelvin
2020-Mar-28 16:43 UTC
[Ocfs2-devel] [RFC PATCH v1 29/50] fs/ocfs2/journal: Use prandom_u32() and not /dev/random for timeout
get_random_bytes() is expensive crypto-quality random numbers. If we're just doing random backoff, prandom_u32() is plenty. (Not to mention fetching 8 bytes of seed material only to reduce it modulo 5000 is a huge waste.) Also, convert timeouts to jiffies at compile time; convert milliseconds to jiffies before picking a random number in the range to take advantage of compile-time constant folding. Signed-off-by: George Spelvin <lkml at sdf.org> Cc: Mark Fasheh <mark at fasheh.com> Cc: Joel Becker <jlbec at evilplan.org> Cc: Joseph Qi <joseph.qi at linux.alibaba.com> Cc: ocfs2-devel at oss.oracle.com --- fs/ocfs2/journal.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c index 68ba354cf3610..939a12e57fa8b 100644 --- a/fs/ocfs2/journal.c +++ b/fs/ocfs2/journal.c @@ -1884,11 +1884,8 @@ int ocfs2_mark_dead_nodes(struct ocfs2_super *osb) */ static inline unsigned long ocfs2_orphan_scan_timeout(void) { - unsigned long time; - - get_random_bytes(&time, sizeof(time)); - time = ORPHAN_SCAN_SCHEDULE_TIMEOUT + (time % 5000); - return msecs_to_jiffies(time); + return msecs_to_jiffies(ORPHAN_SCAN_SCHEDULE_TIMEOUT) + + prandom_u32_max(5 * HZ); } /* -- 2.26.0
Joseph Qi
2020-Mar-30 12:09 UTC
[Ocfs2-devel] [RFC PATCH v1 29/50] fs/ocfs2/journal: Use prandom_u32() and not /dev/random for timeout
Sorry for the late reply since I might miss this mail. On 2019/3/21 11:07, George Spelvin wrote:> get_random_bytes() is expensive crypto-quality random numbers. > If we're just doing random backoff, prandom_u32() is plenty. > > (Not to mention fetching 8 bytes of seed material only to > reduce it modulo 5000 is a huge waste.) > > Also, convert timeouts to jiffies at compile time; convert > milliseconds to jiffies before picking a random number in the > range to take advantage of compile-time constant folding. > > Signed-off-by: George Spelvin <lkml at sdf.org> > Cc: Mark Fasheh <mark at fasheh.com> > Cc: Joel Becker <jlbec at evilplan.org> > Cc: Joseph Qi <joseph.qi at linux.alibaba.com> > Cc: ocfs2-devel at oss.oracle.com > --- > fs/ocfs2/journal.c | 7 ++----- > 1 file changed, 2 insertions(+), 5 deletions(-) > > diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c > index 68ba354cf3610..939a12e57fa8b 100644 > --- a/fs/ocfs2/journal.c > +++ b/fs/ocfs2/journal.c > @@ -1884,11 +1884,8 @@ int ocfs2_mark_dead_nodes(struct ocfs2_super *osb) > */ > static inline unsigned long ocfs2_orphan_scan_timeout(void) > { > - unsigned long time; > - > - get_random_bytes(&time, sizeof(time)); > - time = ORPHAN_SCAN_SCHEDULE_TIMEOUT + (time % 5000); > - return msecs_to_jiffies(time); > + return msecs_to_jiffies(ORPHAN_SCAN_SCHEDULE_TIMEOUT) + > + prandom_u32_max(5 * HZ);Seems better include the prandom_u32_max() into msecs_to_jiffies()? Thanks, Joseph> } > > /* >