Re: [PATCH v2 2/2] ring-buffer: Reuse rb_watermark_hit() for the poll logic
On Wed, 13 Mar 2024 00:38:42 +0900 Masami Hiramatsu (Google) wrote: > On Tue, 12 Mar 2024 09:19:21 -0400 > Steven Rostedt wrote: > > > From: "Steven Rostedt (Google)" > > > > 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) > Thanks! -- Steve
Re: [PATCH v2 2/2] ring-buffer: Reuse rb_watermark_hit() for the poll logic
On Tue, 12 Mar 2024 09:19:21 -0400
Steven Rostedt wrote:
> From: "Steven Rostedt (Google)"
>
> 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)
Thank you,
> Signed-off-by: Steven Rostedt (Google)
> ---
> 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, >full_waiters, poll_table);
>
> - raw_spin_lock_irqsave(_buffer->reader_lock, flags);
> - if (!cpu_buffer->shortest_full ||
> - cpu_buffer->shortest_full > full)
> - cpu_buffer->shortest_full = full;
> - raw_spin_unlock_irqrestore(_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)
[PATCH v2 2/2] ring-buffer: Reuse rb_watermark_hit() for the poll logic
From: "Steven Rostedt (Google)"
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)
---
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, >full_waiters, poll_table);
- raw_spin_lock_irqsave(_buffer->reader_lock, flags);
- if (!cpu_buffer->shortest_full ||
- cpu_buffer->shortest_full > full)
- cpu_buffer->shortest_full = full;
- raw_spin_unlock_irqrestore(_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
