| Message ID | 858d5cb67f299fbdd7a8e7bfab66b426bbe54e0c.1603884539.git.anand.jain@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/4] btrfs: add read_policy latency | expand |
On 10/28/20 9:26 AM, Anand Jain wrote: > Read-policy type 'device' and device flag 'read-preferred': > > The read-policy type device picks the device(s) flagged as > read-preferred for reading chunks of type raid1, raid10, > raid1c3 and raid1c4. > > A system might contain SSD, nvme, iscsi or san lun, and which are all > a non-rotational device, so it is not a good idea to set the read-preferred > automatically. Instead device read-policy along with the read-preferred > flag provides an ability to do it manually. This advance tuning is > useful in more than one situation, for example, > - In heterogeneous-disk volume, it provides an ability to manually choose > the low latency disks for reading. > - Useful for more accurate testing. > - Avoid known problematic device from reading the chunk until it is > replaced (by marking the other good devices as read-preferred). > > Note: > > If the read-policy type is set to 'device', but there isn't any device > which is flagged as read-preferred, then stripe 0 is used for reading. > > The device replace won't migrate the read-preferred flag to the new > replace the target device. > > As of now, this is an in-memory only feature. > > It's pointless to set the read-preferred flag on the missing device, > as IOs aren't submitted to the missing device. > > If there is more than one read-preferred device in a chunk, the read IO > shall go to the stripe 0 (as of now, when depth patches are integrated > we will use the least busy device among the read-preferred devices). > > Usage example: > > Consider a typical two disks raid1. > > Configure devid1 for reading. > > $ echo 1 > devinfo/1/read_preferred > $ cat devinfo/1/read_preferred; cat devinfo/2/read_preferred > 1 > 0 > > $ pwd > /sys/fs/btrfs/12345678-1234-1234-1234-123456789abc > > $ cat read_policy; echo device > ./read_policy; cat read_policy > [pid] device > pid [device] > > Now read IOs are sent to devid 1 (sdb). > > $ echo 3 > /proc/sys/vm/drop_caches; md5sum /btrfs/YkZI > > $ iostat -zy 1 | egrep 'sdb|sdc' (from another terminal) > sdb 50.00 40048.00 0.00 40048 0 > > Change the read-preferred device from devid 1 to devid 2 (sdc). > > $ echo 0 > ./devinfo/1/read_preferred; echo 1 > ./devinfo/2/read_preferred; > > [ 3343.918658] BTRFS info (device sdb): reset read preferred on devid 1 (1334) > [ 3343.919876] BTRFS info (device sdb): set read preferred on devid 2 (1334) > > Further read ios are sent to devid 2 (sdc). > > $ echo 3 > /proc/sys/vm/drop_caches; md5sum /btrfs/YkZI > > $ iostat -zy 1 | egrep 'sdb|sdc' (from another terminal) > sdc 49.00 40048.00 0.00 40048 0 > > Signed-off-by: Anand Jain <anand.jain@oracle.com> > --- > fs/btrfs/sysfs.c | 3 ++- > fs/btrfs/volumes.c | 22 ++++++++++++++++++++++ > fs/btrfs/volumes.h | 1 + > 3 files changed, 25 insertions(+), 1 deletion(-) > > diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c > index 52b4c9bef673..d2a974e1a1c4 100644 > --- a/fs/btrfs/sysfs.c > +++ b/fs/btrfs/sysfs.c > @@ -907,7 +907,8 @@ static bool btrfs_strmatch(const char *given, const char *golden) > } > > /* Must follow the order as in enum btrfs_read_policy */ > -static const char * const btrfs_read_policy_name[] = { "pid", "latency" }; > +static const char * const btrfs_read_policy_name[] = { "pid", "latency", > + "device" }; > > static ssize_t btrfs_read_policy_show(struct kobject *kobj, > struct kobj_attribute *a, char *buf) > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index 48587009b656..7ac675504051 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -5502,6 +5502,25 @@ static int btrfs_find_best_stripe(struct btrfs_fs_info *fs_info, > return best_stripe; > } > > +static int btrfs_find_read_preferred(struct map_lookup *map, int first, int num_stripe) > +{ > + int stripe_index; > + int last = first + num_stripe; > + > + /* > + * If there are more than one read preferred devices, then just pick the > + * first found read preferred device as of now. > + */ > + for (stripe_index = first; stripe_index < last; stripe_index++) { > + if (test_bit(BTRFS_DEV_STATE_READ_PREFERRED, > + &map->stripes[stripe_index].dev->dev_state)) > + return stripe_index; > + } b4 isn't working for me because these patches didn't make it to linux-btrfs proper for some reason, so I could be wrong here, but it looks like this } is off? There's spaces here instead of a tab maybe? If not then just ignore me. Thanks, Josef
>> +static int btrfs_find_read_preferred(struct map_lookup *map, int >> first, int num_stripe) >> +{ >> + int stripe_index; >> + int last = first + num_stripe; >> + >> + /* >> + * If there are more than one read preferred devices, then just >> pick the >> + * first found read preferred device as of now. >> + */ >> + for (stripe_index = first; stripe_index < last; stripe_index++) { >> + if (test_bit(BTRFS_DEV_STATE_READ_PREFERRED, >> + &map->stripes[stripe_index].dev->dev_state)) >> + return stripe_index; >> + } > > b4 isn't working for me because these patches didn't make it to > linux-btrfs proper for some reason, Yep. Since yday I am getting email delivery failure. ----- for recipient address <linux-block@vger.kernel.org> the policy analysis reported: zpostgrey: connect: Connection refused ----- > so I could be wrong here, but it > looks like this } is off? There's spaces here instead of a tab maybe? > If not then just ignore me. Thanks, Yeah tab is ok. Its just in the email. Thanks, Anand > Josef
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c index 52b4c9bef673..d2a974e1a1c4 100644 --- a/fs/btrfs/sysfs.c +++ b/fs/btrfs/sysfs.c @@ -907,7 +907,8 @@ static bool btrfs_strmatch(const char *given, const char *golden) } /* Must follow the order as in enum btrfs_read_policy */ -static const char * const btrfs_read_policy_name[] = { "pid", "latency" }; +static const char * const btrfs_read_policy_name[] = { "pid", "latency", + "device" }; static ssize_t btrfs_read_policy_show(struct kobject *kobj, struct kobj_attribute *a, char *buf) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 48587009b656..7ac675504051 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -5502,6 +5502,25 @@ static int btrfs_find_best_stripe(struct btrfs_fs_info *fs_info, return best_stripe; } +static int btrfs_find_read_preferred(struct map_lookup *map, int first, int num_stripe) +{ + int stripe_index; + int last = first + num_stripe; + + /* + * If there are more than one read preferred devices, then just pick the + * first found read preferred device as of now. + */ + for (stripe_index = first; stripe_index < last; stripe_index++) { + if (test_bit(BTRFS_DEV_STATE_READ_PREFERRED, + &map->stripes[stripe_index].dev->dev_state)) + return stripe_index; + } + + /* If there is no read preferred device then just use the first stripe */ + return first; +} + static int find_live_mirror(struct btrfs_fs_info *fs_info, struct map_lookup *map, int first, int dev_replace_is_ongoing) @@ -5536,6 +5555,9 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info, preferred_mirror = btrfs_find_best_stripe(fs_info, map, first, num_stripes); break; + case BTRFS_READ_POLICY_DEVICE: + preferred_mirror = btrfs_find_read_preferred(map, first, num_stripes); + break; } if (dev_replace_is_ongoing && diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h index f1cbbb18f5ef..1448adb8993d 100644 --- a/fs/btrfs/volumes.h +++ b/fs/btrfs/volumes.h @@ -219,6 +219,7 @@ enum btrfs_chunk_allocation_policy { enum btrfs_read_policy { BTRFS_READ_POLICY_PID, BTRFS_READ_POLICY_LATENCY, + BTRFS_READ_POLICY_DEVICE, BTRFS_NR_READ_POLICY, };
Read-policy type 'device' and device flag 'read-preferred': The read-policy type device picks the device(s) flagged as read-preferred for reading chunks of type raid1, raid10, raid1c3 and raid1c4. A system might contain SSD, nvme, iscsi or san lun, and which are all a non-rotational device, so it is not a good idea to set the read-preferred automatically. Instead device read-policy along with the read-preferred flag provides an ability to do it manually. This advance tuning is useful in more than one situation, for example, - In heterogeneous-disk volume, it provides an ability to manually choose the low latency disks for reading. - Useful for more accurate testing. - Avoid known problematic device from reading the chunk until it is replaced (by marking the other good devices as read-preferred). Note: If the read-policy type is set to 'device', but there isn't any device which is flagged as read-preferred, then stripe 0 is used for reading. The device replace won't migrate the read-preferred flag to the new replace the target device. As of now, this is an in-memory only feature. It's pointless to set the read-preferred flag on the missing device, as IOs aren't submitted to the missing device. If there is more than one read-preferred device in a chunk, the read IO shall go to the stripe 0 (as of now, when depth patches are integrated we will use the least busy device among the read-preferred devices). Usage example: Consider a typical two disks raid1. Configure devid1 for reading. $ echo 1 > devinfo/1/read_preferred $ cat devinfo/1/read_preferred; cat devinfo/2/read_preferred 1 0 $ pwd /sys/fs/btrfs/12345678-1234-1234-1234-123456789abc $ cat read_policy; echo device > ./read_policy; cat read_policy [pid] device pid [device] Now read IOs are sent to devid 1 (sdb). $ echo 3 > /proc/sys/vm/drop_caches; md5sum /btrfs/YkZI $ iostat -zy 1 | egrep 'sdb|sdc' (from another terminal) sdb 50.00 40048.00 0.00 40048 0 Change the read-preferred device from devid 1 to devid 2 (sdc). $ echo 0 > ./devinfo/1/read_preferred; echo 1 > ./devinfo/2/read_preferred; [ 3343.918658] BTRFS info (device sdb): reset read preferred on devid 1 (1334) [ 3343.919876] BTRFS info (device sdb): set read preferred on devid 2 (1334) Further read ios are sent to devid 2 (sdc). $ echo 3 > /proc/sys/vm/drop_caches; md5sum /btrfs/YkZI $ iostat -zy 1 | egrep 'sdb|sdc' (from another terminal) sdc 49.00 40048.00 0.00 40048 0 Signed-off-by: Anand Jain <anand.jain@oracle.com> --- fs/btrfs/sysfs.c | 3 ++- fs/btrfs/volumes.c | 22 ++++++++++++++++++++++ fs/btrfs/volumes.h | 1 + 3 files changed, 25 insertions(+), 1 deletion(-)