[PATCH 0/2] block : Patches related to io_polling

[PATCH 0/2] block : Patches related to io_polling

[Stephen Bates]

While profiling the performance of the io_poll feature of the blk-mq
section of the block layer I found it useful to add another entry to
the io_poll stats counters. I also found it really useful to be able
to zero the stats counters by echoing into the relevant sysfs entry.

These two patches are based off commit 0eadf37afc in Jen's
for-4.9/block. I am not sure if that is the right repo and can rebase
if necessary.

In full disclosure the zeroing patch is based heavily on a code
snippet Jens send me a few months ago.

Stephen Bates (2):
  Add poll_considered statistic
  Enable zeroing of io_poll statistics

 block/blk-core.c       |  8 ++++++--
 block/blk-mq-sysfs.c   | 15 +++++++++++++--
 include/linux/blk-mq.h |  1 +
 3 files changed, 20 insertions(+), 4 deletions(-)

--
2.1.4

[PATCH 1/2] Add poll_considered statistic

[Stephen Bates]

In order to help determine the effectiveness of polling in a running
system it is usful to determine the ratio of how often the poll
function is called vs how often the completion is checked. For this
reason we add a poll_considered variable and add it to the sysfs entry
for io_poll.

Signed-off-by: Stephen Bates <sbates@raithlin.com>
---
 block/blk-core.c       | 8 ++++++--
 block/blk-mq-sysfs.c   | 4 +++-
 include/linux/blk-mq.h | 1 +
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 34ff808..14d7c07 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -3307,19 +3307,23 @@ bool blk_poll(struct request_queue *q, blk_qc_t cookie)
 {
 	struct blk_plug *plug;
 	long state;
+	unsigned int queue_num;
+	struct blk_mq_hw_ctx *hctx;
 
 	if (!q->mq_ops || !q->mq_ops->poll || !blk_qc_t_valid(cookie) ||
 	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
 		return false;
 
+	queue_num = blk_qc_t_to_queue_num(cookie);
+	hctx = q->queue_hw_ctx[queue_num];
+	hctx->poll_considered++;
+
 	plug = current->plug;
 	if (plug)
 		blk_flush_plug_list(plug, false);
 
 	state = current->state;
 	while (!need_resched()) {
-		unsigned int queue_num = blk_qc_t_to_queue_num(cookie);
-		struct blk_mq_hw_ctx *hctx = q->queue_hw_ctx[queue_num];
 		int ret;
 
 		hctx->poll_invoked++;
diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index fe822aa..ea8c3f5 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -176,7 +176,9 @@ static ssize_t blk_mq_sysfs_rq_list_show(struct blk_mq_ctx *ctx, char *page)
 
 static ssize_t blk_mq_hw_sysfs_poll_show(struct blk_mq_hw_ctx *hctx, char *page)
 {
-	return sprintf(page, "invoked=%lu, success=%lu\n", hctx->poll_invoked, hctx->poll_success);
+	return sprintf(page, "considered=%lu, invoked=%lu, success=%lu\n",
+		       hctx->poll_considered, hctx->poll_invoked,
+		       hctx->poll_success);
 }
 
 static ssize_t blk_mq_hw_sysfs_queued_show(struct blk_mq_hw_ctx *hctx,
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index e1544f0..7710f79 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -61,6 +61,7 @@ struct blk_mq_hw_ctx {
 	struct blk_mq_cpu_notifier	cpu_notifier;
 	struct kobject		kobj;
 
+	unsigned long		poll_considered;
 	unsigned long		poll_invoked;
 	unsigned long		poll_success;
 };
-- 
2.1.4

[PATCH 2/2] Enable zeroing of io_poll statistics

[Stephen Bates]

Allow the io_poll statistics to be zeroed to make for easier logging
of polling event.

Signed-off-by: Stephen Bates <sbates@raithlin.com>
---
 block/blk-mq-sysfs.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index ea8c3f5..ac5160e 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -181,6 +181,14 @@ static ssize_t blk_mq_hw_sysfs_poll_show(struct blk_mq_hw_ctx *hctx, char *page)
 		       hctx->poll_success);
 }
 
+static ssize_t blk_mq_hw_sysfs_poll_store(struct blk_mq_hw_ctx *hctx,
+					  const char *page, size_t size)
+{
+	hctx->poll_considered = hctx->poll_invoked = hctx->poll_success = 0;
+
+	return size;
+}
+
 static ssize_t blk_mq_hw_sysfs_queued_show(struct blk_mq_hw_ctx *hctx,
 					   char *page)
 {
@@ -303,8 +311,9 @@ static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_cpus = {
 	.show = blk_mq_hw_sysfs_cpus_show,
 };
 static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_poll = {
-	.attr = {.name = "io_poll", .mode = S_IRUGO },
+	.attr = {.name = "io_poll", .mode = S_IWUSR | S_IRUGO },
 	.show = blk_mq_hw_sysfs_poll_show,
+	.store = blk_mq_hw_sysfs_poll_store,
 };
 
 static struct attribute *default_hw_ctx_attrs[] = {
-- 
2.1.4

Re: [PATCH 0/2] block : Patches related to io_polling

[Christoph Hellwig]

Hi Stephen,

the series looks reasonable to me:

Acked-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 0/2] block : Patches related to io_polling

[Jens Axboe]

On 09/13/2016 12:23 PM, Stephen Bates wrote:
> While profiling the performance of the io_poll feature of the blk-mq
> section of the block layer I found it useful to add another entry to
> the io_poll stats counters. I also found it really useful to be able
> to zero the stats counters by echoing into the relevant sysfs entry.
>
> These two patches are based off commit 0eadf37afc in Jen's
> for-4.9/block. I am not sure if that is the right repo and can rebase
> if necessary.
>
> In full disclosure the zeroing patch is based heavily on a code
> snippet Jens send me a few months ago.

Thanks Stephen, added for 4.9.

-- 
Jens Axboe