On Fri, May 16, 2025 at 2:19 AM Jens Axboe <ax...@kernel.dk> wrote:
>
> On 5/15/25 12:16 AM, Jason Xing wrote:
> > From: Jason Xing <kernelx...@tencent.com>
> >
> > In this version, only support dumping the counter for buffer full and
> > implement the framework of how it works.
> >
> > Users can pass certain flag to fetch what field/statistics they expect
> > to know. Each time it only returns one result. So do not pass multiple
> > flags.
> >
> > Reviewed-by: Yushan Zhou <katrinz...@tencent.com>
> > Signed-off-by: Jason Xing <kernelx...@tencent.com>
> > ---
> > v2
> > 1. refactor relay_dump() and make it only return a pure size_t result
> > of the value that users specifies.
> > 2. revise the commit log.
> > ---
> > include/linux/relay.h | 7 +++++++
> > kernel/relay.c | 31 +++++++++++++++++++++++++++++++
> > 2 files changed, 38 insertions(+)
> >
> > diff --git a/include/linux/relay.h b/include/linux/relay.h
> > index ce7a1b396872..3fb285716e34 100644
> > --- a/include/linux/relay.h
> > +++ b/include/linux/relay.h
> > @@ -31,6 +31,12 @@
> > /*
> > * Relay buffer statistics dump
> > */
> > +enum {
> > + RELAY_DUMP_BUF_FULL = (1 << 0),
> > +
> > + RELAY_DUMP_LAST = RELAY_DUMP_BUF_FULL,
> > +};
> > +
> > struct rchan_buf_stats
> > {
> > unsigned int full_count; /* counter for buffer full */
> > @@ -167,6 +173,7 @@ struct rchan *relay_open(const char *base_filename,
> > void *private_data);
> > extern void relay_close(struct rchan *chan);
> > extern void relay_flush(struct rchan *chan);
> > +extern size_t relay_dump(struct rchan *chan, int flags);
> > extern void relay_subbufs_consumed(struct rchan *chan,
> > unsigned int cpu,
> > size_t consumed);
> > diff --git a/kernel/relay.c b/kernel/relay.c
> > index eb3f630f3896..f47fc750e559 100644
> > --- a/kernel/relay.c
> > +++ b/kernel/relay.c
> > @@ -701,6 +701,37 @@ void relay_flush(struct rchan *chan)
> > }
> > EXPORT_SYMBOL_GPL(relay_flush);
> >
> > +/**
> > + * relay_dump - dump channel buffer statistics
> > + * @chan: the channel
> > + * @flags: select particular information to dump
> > + *
> > + * Returns the count of certain field that caller specifies.
> > + */
> > +size_t relay_dump(struct rchan *chan, int flags)
> > +{
> > + unsigned int i, count = 0;
> > + struct rchan_buf *rbuf;
> > +
> > + if (!chan || flags > RELAY_DUMP_LAST)
> > + return 0;
> > +
> > + if (chan->is_global) {
> > + rbuf = *per_cpu_ptr(chan->buf, 0);
> > + if (flags & RELAY_DUMP_BUF_FULL)
> > + count = rbuf->stats.full_count;
> > + } else {
> > + for_each_online_cpu(i) {
> > + if ((rbuf = *per_cpu_ptr(chan->buf, i)))
> > + if (flags & RELAY_DUMP_BUF_FULL)
> > + count += rbuf->stats.full_count;
>
> Kernel tends to avoid the rolled-into-one assignment and check, it's
> easy to misread. This:
>
> rbuf = *per_cpu_ptr(chan->buf, i);
> if (rbuf && flags & RELAY_DUMP_BUF_FULL)
> count += rbuf->stats.full_count;
>
> reads much easier. IMHO.
Agreed. Thanks. I will rewrite this part in V3 :)
Thanks,
Jason
>
> --
> Jens Axboe
