Messages in this thread | | | Date | Wed, 26 Jan 2022 18:08:12 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH v3] printk: ringbuffer: Improve prb_next_seq() performance |
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On Fri 2022-01-21 15:14:41, John Ogness wrote: > Hi Mukesh, > > Thanks for pushing this. I think it got lost somewhere. I have a couple > very minor non-functional change requests.
Yes, thanks for pushing this. I have somehow lost this patch on my radar.
> On 2022-01-21, Mukesh Ojha <quic_mojha@quicinc.com> wrote: > > From: Petr Mladek <pmladek@suse.com> > > > > prb_next_seq() always iterates from the first known sequence number. > > In the worst case, it might loop 8k times for 256kB buffer, > > 15k times for 512kB buffer, and 64k times for 2MB buffer. > > > > It was reported that pooling and reading using syslog interface > > ^^^^^^^ polling > > > might occupy 50% of CPU. > > > > Speedup the search by storing @id of the last finalized descriptor. > > > > The loop is still needed because the @id is stored and read in the best > > effort way. An atomic variable is used to keep the @id consistent. > > But the stores and reads are not serialized against each other. > > The descriptor could get reused in the meantime. The related sequence > > number will be used only when it is still valid. > > > > An invalid value should be read _only_ when there is a flood of messages > > and the ringbuffer is rapidly reused. The performance is the least > > problem in this case. > > > > Link: https://lore.kernel.org/lkml/YXlddJxLh77DKfIO@alley/T/#m43062e8b2a17f8dbc8c6ccdb8851fb0dbaabbb14 > > Reported-by: Chunlei Wang <chunlei.wang@mediatek.com> > > Signed-off-by: Petr Mladek <pmladek@suse.com> > > Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com> > > --- > > Changes against v2: > > Added the hunk suggested by John > > > Petr can probably just make the changes when committing. I am not > requesting a v4. > > @Petr: Feel free to add: > > Reviewed-by: John Ogness <john.ogness@linutronix.de>
I made the changes suggested by John. Also I have reverted few more formatting changes. The result is basically v2 + the hunk suggested by John.
The patch is committed in printk/linux.git, branch rework/fast-next-seq. I am going to queue it for 5.18.
Best Regards, Petr
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