From: "Steven Rostedt (Google)" <[email protected]>
The check for knowing if the poll should wait or not is basically the
exact same logic as rb_watermark_hit(). The only difference is that
rb_watermark_hit() also handles the !full case. But for the full case, the
logic is the same. Just call that instead of duplicating the code in
ring_buffer_poll_wait().
Signed-off-by: Steven Rostedt (Google) <[email protected]>
---
kernel/trace/ring_buffer.c | 21 +++++++--------------
1 file changed, 7 insertions(+), 14 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index adfe603a769b..857803e8cf07 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -959,25 +959,18 @@ __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu,
}
if (full) {
- unsigned long flags;
-
poll_wait(filp, &rbwork->full_waiters, poll_table);
- raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
- if (!cpu_buffer->shortest_full ||
- cpu_buffer->shortest_full > full)
- cpu_buffer->shortest_full = full;
- raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
- if (full_hit(buffer, cpu, full))
+ if (rb_watermark_hit(buffer, cpu, full))
return EPOLLIN | EPOLLRDNORM;
/*
* Only allow full_waiters_pending update to be seen after
- * the shortest_full is set. If the writer sees the
- * full_waiters_pending flag set, it will compare the
- * amount in the ring buffer to shortest_full. If the amount
- * in the ring buffer is greater than the shortest_full
- * percent, it will call the irq_work handler to wake up
- * this list. The irq_handler will reset shortest_full
+ * the shortest_full is set (in rb_watermark_hit). If the
+ * writer sees the full_waiters_pending flag set, it will
+ * compare the amount in the ring buffer to shortest_full.
+ * If the amount in the ring buffer is greater than the
+ * shortest_full percent, it will call the irq_work handler
+ * to wake up this list. The irq_handler will reset shortest_full
* back to zero. That's done under the reader_lock, but
* the below smp_mb() makes sure that the update to
* full_waiters_pending doesn't leak up into the above.
--
2.43.0
On Tue, 12 Mar 2024 09:19:21 -0400
Steven Rostedt <[email protected]> wrote:
> From: "Steven Rostedt (Google)" <[email protected]>
>
> The check for knowing if the poll should wait or not is basically the
> exact same logic as rb_watermark_hit(). The only difference is that
> rb_watermark_hit() also handles the !full case. But for the full case, the
> logic is the same. Just call that instead of duplicating the code in
> ring_buffer_poll_wait().
>
This changes a bit (e.g. adding pagebusy check) but basically that should
be there. And new version appears to be consistent between ring_buffer_wait()
and ring_buffer_poll_wait(). So looks good to me.
Reviewed-by: Masami Hiramatsu (Google) <[email protected]>
Thank you,
> Signed-off-by: Steven Rostedt (Google) <[email protected]>
> ---
> kernel/trace/ring_buffer.c | 21 +++++++--------------
> 1 file changed, 7 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index adfe603a769b..857803e8cf07 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -959,25 +959,18 @@ __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu,
> }
>
> if (full) {
> - unsigned long flags;
> -
> poll_wait(filp, &rbwork->full_waiters, poll_table);
>
> - raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
> - if (!cpu_buffer->shortest_full ||
> - cpu_buffer->shortest_full > full)
> - cpu_buffer->shortest_full = full;
> - raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
> - if (full_hit(buffer, cpu, full))
> + if (rb_watermark_hit(buffer, cpu, full))
> return EPOLLIN | EPOLLRDNORM;
> /*
> * Only allow full_waiters_pending update to be seen after
> - * the shortest_full is set. If the writer sees the
> - * full_waiters_pending flag set, it will compare the
> - * amount in the ring buffer to shortest_full. If the amount
> - * in the ring buffer is greater than the shortest_full
> - * percent, it will call the irq_work handler to wake up
> - * this list. The irq_handler will reset shortest_full
> + * the shortest_full is set (in rb_watermark_hit). If the
> + * writer sees the full_waiters_pending flag set, it will
> + * compare the amount in the ring buffer to shortest_full.
> + * If the amount in the ring buffer is greater than the
> + * shortest_full percent, it will call the irq_work handler
> + * to wake up this list. The irq_handler will reset shortest_full
> * back to zero. That's done under the reader_lock, but
> * the below smp_mb() makes sure that the update to
> * full_waiters_pending doesn't leak up into the above.
> --
> 2.43.0
>
>
>
--
Masami Hiramatsu (Google) <[email protected]>
On Wed, 13 Mar 2024 00:38:42 +0900
Masami Hiramatsu (Google) <[email protected]> wrote:
> On Tue, 12 Mar 2024 09:19:21 -0400
> Steven Rostedt <[email protected]> wrote:
>
> > From: "Steven Rostedt (Google)" <[email protected]>
> >
> > The check for knowing if the poll should wait or not is basically the
> > exact same logic as rb_watermark_hit(). The only difference is that
> > rb_watermark_hit() also handles the !full case. But for the full case, the
> > logic is the same. Just call that instead of duplicating the code in
> > ring_buffer_poll_wait().
> >
>
> This changes a bit (e.g. adding pagebusy check) but basically that should
> be there. And new version appears to be consistent between ring_buffer_wait()
> and ring_buffer_poll_wait(). So looks good to me.
The pagebusy check is an optimization. As if it is true, it means the
writer is still on the reader_page and there's no sub-buffers available. It
just prevents having to do the calculation of the buffer-percentage filled
(what's done by the full_hit() logic).
>
> Reviewed-by: Masami Hiramatsu (Google) <[email protected]>
>
Thanks!
-- Steve