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[PATCH 1/3] md/raid10: optimize fix_read_error

linan666@huaweicloud.com posted 3 patches 2 years, 7 months ago
[PATCH 1/3] md/raid10: optimize fix_read_error
Posted by linan666@huaweicloud.com 2 years, 7 months ago 
From: Li Nan <linan122@huawei.com>

We dereference r10_bio->read_slot too many times in fix_read_error().
Optimize it by using a variable to store read_slot.

Signed-off-by: Li Nan <linan122@huawei.com>
---
 drivers/md/raid10.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 381c21f7fb06..94ae294c8a3c 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2725,10 +2725,10 @@ static int r10_sync_page_io(struct md_rdev *rdev, sector_t sector,
 static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10bio *r10_bio)
 {
 	int sect = 0; /* Offset from r10_bio->sector */
-	int sectors = r10_bio->sectors;
+	int sectors = r10_bio->sectors, slot = r10_bio->read_slot;
 	struct md_rdev *rdev;
 	int max_read_errors = atomic_read(&mddev->max_corr_read_errors);
-	int d = r10_bio->devs[r10_bio->read_slot].devnum;
+	int d = r10_bio->devs[slot].devnum;
 
 	/* still own a reference to this rdev, so it cannot
 	 * have been cleared recently.
@@ -2749,13 +2749,13 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 		pr_notice("md/raid10:%s: %pg: Failing raid device\n",
 			  mdname(mddev), rdev->bdev);
 		md_error(mddev, rdev);
-		r10_bio->devs[r10_bio->read_slot].bio = IO_BLOCKED;
+		r10_bio->devs[slot].bio = IO_BLOCKED;
 		return;
 	}
 
 	while(sectors) {
 		int s = sectors;
-		int sl = r10_bio->read_slot;
+		int sl = slot;
 		int success = 0;
 		int start;
 
@@ -2790,7 +2790,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 			sl++;
 			if (sl == conf->copies)
 				sl = 0;
-		} while (!success && sl != r10_bio->read_slot);
+		} while (!success && sl != slot);
 		rcu_read_unlock();
 
 		if (!success) {
@@ -2798,16 +2798,16 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 			 * as bad on the first device to discourage future
 			 * reads.
 			 */
-			int dn = r10_bio->devs[r10_bio->read_slot].devnum;
+			int dn = r10_bio->devs[slot].devnum;
 			rdev = conf->mirrors[dn].rdev;
 
 			if (!rdev_set_badblocks(
 				    rdev,
-				    r10_bio->devs[r10_bio->read_slot].addr
+				    r10_bio->devs[slot].addr
 				    + sect,
 				    s, 0)) {
 				md_error(mddev, rdev);
-				r10_bio->devs[r10_bio->read_slot].bio
+				r10_bio->devs[slot].bio
 					= IO_BLOCKED;
 			}
 			break;
@@ -2816,7 +2816,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 		start = sl;
 		/* write it back and re-read */
 		rcu_read_lock();
-		while (sl != r10_bio->read_slot) {
+		while (sl != slot) {
 			if (sl==0)
 				sl = conf->copies;
 			sl--;
@@ -2850,7 +2850,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 			rcu_read_lock();
 		}
 		sl = start;
-		while (sl != r10_bio->read_slot) {
+		while (sl != slot) {
 			if (sl==0)
 				sl = conf->copies;
 			sl--;
-- 
2.39.2
Re: [PATCH 1/3] md/raid10: optimize fix_read_error
Posted by Yu Kuai 2 years, 7 months ago 
Hi,

在 2023/06/24 1:32, linan666@huaweicloud.com 写道:
> From: Li Nan <linan122@huawei.com>
> 
> We dereference r10_bio->read_slot too many times in fix_read_error().
> Optimize it by using a variable to store read_slot.
> 

Other than a nit below, this patch LGTM.

Reviewed-by: Yu Kuai <yukuai3@huawei.com>

> Signed-off-by: Li Nan <linan122@huawei.com>
> ---
>   drivers/md/raid10.c | 20 ++++++++++----------
>   1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 381c21f7fb06..94ae294c8a3c 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -2725,10 +2725,10 @@ static int r10_sync_page_io(struct md_rdev *rdev, sector_t sector,
>   static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10bio *r10_bio)
>   {
>   	int sect = 0; /* Offset from r10_bio->sector */
> -	int sectors = r10_bio->sectors;
> +	int sectors = r10_bio->sectors, slot = r10_bio->read_slot;
>   	struct md_rdev *rdev;
>   	int max_read_errors = atomic_read(&mddev->max_corr_read_errors);
> -	int d = r10_bio->devs[r10_bio->read_slot].devnum;
> +	int d = r10_bio->devs[slot].devnum;
>   
>   	/* still own a reference to this rdev, so it cannot
>   	 * have been cleared recently.
> @@ -2749,13 +2749,13 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
>   		pr_notice("md/raid10:%s: %pg: Failing raid device\n",
>   			  mdname(mddev), rdev->bdev);
>   		md_error(mddev, rdev);
> -		r10_bio->devs[r10_bio->read_slot].bio = IO_BLOCKED;
> +		r10_bio->devs[slot].bio = IO_BLOCKED;
>   		return;
>   	}
>   
>   	while(sectors) {
>   		int s = sectors;
> -		int sl = r10_bio->read_slot;
> +		int sl = slot;
>   		int success = 0;
>   		int start;
>   
> @@ -2790,7 +2790,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
>   			sl++;
>   			if (sl == conf->copies)
>   				sl = 0;
> -		} while (!success && sl != r10_bio->read_slot);
> +		} while (!success && sl != slot);
>   		rcu_read_unlock();
>   
>   		if (!success) {
> @@ -2798,16 +2798,16 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
>   			 * as bad on the first device to discourage future
>   			 * reads.
>   			 */
> -			int dn = r10_bio->devs[r10_bio->read_slot].devnum;
> +			int dn = r10_bio->devs[slot].devnum;
>   			rdev = conf->mirrors[dn].rdev;
>   
>   			if (!rdev_set_badblocks(
>   				    rdev,
> -				    r10_bio->devs[r10_bio->read_slot].addr
> +				    r10_bio->devs[slot].addr
>   				    + sect,
>   				    s, 0)) {
>   				md_error(mddev, rdev);
> -				r10_bio->devs[r10_bio->read_slot].bio
> +				r10_bio->devs[slot].bio
>   					= IO_BLOCKED;

There is no need to split lines now.

Thanks,
Kuai
>   			}
>   			break;
> @@ -2816,7 +2816,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
>   		start = sl;
>   		/* write it back and re-read */
>   		rcu_read_lock();
> -		while (sl != r10_bio->read_slot) {
> +		while (sl != slot) {
>   			if (sl==0)
>   				sl = conf->copies;
>   			sl--;
> @@ -2850,7 +2850,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
>   			rcu_read_lock();
>   		}
>   		sl = start;
> -		while (sl != r10_bio->read_slot) {
> +		while (sl != slot) {
>   			if (sl==0)
>   				sl = conf->copies;
>   			sl--;
>
Re: [PATCH 1/3] md/raid10: optimize fix_read_error
Posted by Paul Menzel 2 years, 7 months ago 
Dear Li,


Thank you for your patch.

Am 23.06.23 um 19:32 schrieb linan666@huaweicloud.com:
> From: Li Nan <linan122@huawei.com>
> 
> We dereference r10_bio->read_slot too many times in fix_read_error().
> Optimize it by using a variable to store read_slot.

I am always cautious reading about optimizations without any benchmarks 
or object code analysis. Although your explanation makes sense, did you 
check, that performance didn’t decrease in some way? (Maybe the compiler 
even generates the same code.)


Kind regards,

Paul


> Signed-off-by: Li Nan <linan122@huawei.com>
> ---
>   drivers/md/raid10.c | 20 ++++++++++----------
>   1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 381c21f7fb06..94ae294c8a3c 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -2725,10 +2725,10 @@ static int r10_sync_page_io(struct md_rdev *rdev, sector_t sector,
>   static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10bio *r10_bio)
>   {
>   	int sect = 0; /* Offset from r10_bio->sector */
> -	int sectors = r10_bio->sectors;
> +	int sectors = r10_bio->sectors, slot = r10_bio->read_slot;
>   	struct md_rdev *rdev;
>   	int max_read_errors = atomic_read(&mddev->max_corr_read_errors);
> -	int d = r10_bio->devs[r10_bio->read_slot].devnum;
> +	int d = r10_bio->devs[slot].devnum;
>   
>   	/* still own a reference to this rdev, so it cannot
>   	 * have been cleared recently.
> @@ -2749,13 +2749,13 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
>   		pr_notice("md/raid10:%s: %pg: Failing raid device\n",
>   			  mdname(mddev), rdev->bdev);
>   		md_error(mddev, rdev);
> -		r10_bio->devs[r10_bio->read_slot].bio = IO_BLOCKED;
> +		r10_bio->devs[slot].bio = IO_BLOCKED;
>   		return;
>   	}
>   
>   	while(sectors) {
>   		int s = sectors;
> -		int sl = r10_bio->read_slot;
> +		int sl = slot;
>   		int success = 0;
>   		int start;
>   
> @@ -2790,7 +2790,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
>   			sl++;
>   			if (sl == conf->copies)
>   				sl = 0;
> -		} while (!success && sl != r10_bio->read_slot);
> +		} while (!success && sl != slot);
>   		rcu_read_unlock();
>   
>   		if (!success) {
> @@ -2798,16 +2798,16 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
>   			 * as bad on the first device to discourage future
>   			 * reads.
>   			 */
> -			int dn = r10_bio->devs[r10_bio->read_slot].devnum;
> +			int dn = r10_bio->devs[slot].devnum;
>   			rdev = conf->mirrors[dn].rdev;
>   
>   			if (!rdev_set_badblocks(
>   				    rdev,
> -				    r10_bio->devs[r10_bio->read_slot].addr
> +				    r10_bio->devs[slot].addr
>   				    + sect,
>   				    s, 0)) {
>   				md_error(mddev, rdev);
> -				r10_bio->devs[r10_bio->read_slot].bio
> +				r10_bio->devs[slot].bio
>   					= IO_BLOCKED;
>   			}
>   			break;
> @@ -2816,7 +2816,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
>   		start = sl;
>   		/* write it back and re-read */
>   		rcu_read_lock();
> -		while (sl != r10_bio->read_slot) {
> +		while (sl != slot) {
>   			if (sl==0)
>   				sl = conf->copies;
>   			sl--;
> @@ -2850,7 +2850,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
>   			rcu_read_lock();
>   		}
>   		sl = start;
> -		while (sl != r10_bio->read_slot) {
> +		while (sl != slot) {
>   			if (sl==0)
>   				sl = conf->copies;
>   			sl--;
Re: [PATCH 1/3] md/raid10: optimize fix_read_error
Posted by Li Nan 2 years, 7 months ago 

在 2023/6/23 18:03, Paul Menzel 写道:
> Dear Li,
> 
> 
> Thank you for your patch.
> 
> Am 23.06.23 um 19:32 schrieb linan666@huaweicloud.com:
>> From: Li Nan <linan122@huawei.com>
>>
>> We dereference r10_bio->read_slot too many times in fix_read_error().
>> Optimize it by using a variable to store read_slot.
> 
> I am always cautious reading about optimizations without any benchmarks 
> or object code analysis. Although your explanation makes sense, did you 
> check, that performance didn’t decrease in some way? (Maybe the compiler 
> even generates the same code.)
> 
> 
> Kind regards,
> 
> Paul
> 
> 

Compared assembly code before and after optimization:
  - With gcc 8.3.0, both are consistent.
  - With gcc 12.2.1, 'r10_bio->read_slot' mostly uses r10bio dirctly:
      2853    while (sl != r10_bio->read_slot) {
        0xffffffff8213f2a0 <+1328>:  cmp    %r14d,0x38(%rbp)

    'slot' is mostly saved to a register individually:
      2819    while (sl != slot) {
        0xffffffff8213f08a <+794>:   cmp    %r14d,%ebx

I have not tested the performance, and it won't bring significant 
performance optimization, which can also be seen from the analysis of 
the assembly code. In fact, I just want to make code more readable.

-- 
Thanks,
Nan

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