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([2620:10d:c091:480::1:a066]) by smtp.gmail.com with ESMTPSA id 184sm13672930qkg.92.2021.01.19.11.36.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 Jan 2021 11:36:58 -0800 (PST) Subject: Re: [PATCH v3 1/4] btrfs: add read_policy latency To: Anand Jain , linux-btrfs@vger.kernel.org Cc: dsterba@suse.com References: <64bb4905dc4b77e9fa22d8ba2635a36d15a33469.1610324448.git.anand.jain@oracle.com> From: Josef Bacik Message-ID: Date: Tue, 19 Jan 2021 14:36:57 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <64bb4905dc4b77e9fa22d8ba2635a36d15a33469.1610324448.git.anand.jain@oracle.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 1/11/21 4:41 AM, Anand Jain wrote: > The read policy type latency routes the read IO based on the historical > average wait-time experienced by the read IOs through the individual > device. This patch obtains the historical read IO stats from the kernel > block layer and calculates its average. > > Example usage: > echo "latency" > /sys/fs/btrfs/$uuid/read_policy > > Signed-off-by: Anand Jain > --- > v3: The block layer commit 0d02129e76ed (block: merge struct block_device and > struct hd_struct) has changed the first argument in the function > part_stat_read_all() in 5.11-rc1. So the compilation will fail. This patch > fixes it. > Commit log updated. > > v2: Use btrfs_debug_rl() instead of btrfs_info_rl() > It is better we have this debug until we test this on at least few > hardwares. > Drop the unrelated changes. > Update change log. > > v1: Drop part_stat_read_all instead use part_stat_read > Drop inflight > > > fs/btrfs/sysfs.c | 3 ++- > fs/btrfs/volumes.c | 38 ++++++++++++++++++++++++++++++++++++++ > fs/btrfs/volumes.h | 2 ++ > 3 files changed, 42 insertions(+), 1 deletion(-) > > diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c > index 19b9fffa2c9c..96ca7bef6357 100644 > --- a/fs/btrfs/sysfs.c > +++ b/fs/btrfs/sysfs.c > @@ -915,7 +915,8 @@ static bool strmatch(const char *buffer, const char *string) > return false; > } > > -static const char * const btrfs_read_policy_name[] = { "pid" }; > +/* Must follow the order as in enum btrfs_read_policy */ > +static const char * const btrfs_read_policy_name[] = { "pid", "latency" }; > > 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 f4037a6bd926..f7a0a83d2cd4 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -14,6 +14,7 @@ > #include > #include > #include > +#include > #include "misc.h" > #include "ctree.h" > #include "extent_map.h" > @@ -5490,6 +5491,39 @@ int btrfs_is_parity_mirror(struct btrfs_fs_info *fs_info, u64 logical, u64 len) > return ret; > } > > +static int btrfs_find_best_stripe(struct btrfs_fs_info *fs_info, > + struct map_lookup *map, int first, > + int num_stripe) > +{ > + u64 est_wait = 0; > + int best_stripe = 0; > + int index; > + > + for (index = first; index < first + num_stripe; index++) { > + u64 read_wait; > + u64 avg_wait = 0; > + unsigned long read_ios; > + struct btrfs_device *device = map->stripes[index].dev; > + > + read_wait = part_stat_read(device->bdev, nsecs[READ]); > + read_ios = part_stat_read(device->bdev, ios[READ]); > + > + if (read_wait && read_ios && read_wait >= read_ios) > + avg_wait = div_u64(read_wait, read_ios); > + else > + btrfs_debug_rl(device->fs_devices->fs_info, You can just use fs_info here, you already have it. I'm not in love with doing this check every time, I'd rather cache the results somewhere. However if we're read-only I can't think of a mechanism we could piggy back on, RW we could just do it every transaction commit. Fix the fs_info thing and you can add Reviewed-by: Josef Bacik Thanks, Josef