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Message-ID: <f448f66b-7a91-4281-8f77-159541cbacff@redhat.com>
Date: Wed, 17 Jul 2024 13:37:56 -0400
From: Waiman Long <longman@...hat.com>
To: "tj@...nel.org" <tj@...nel.org>, Boy Wu (吳勃誼)
<Boy.Wu@...iatek.com>
Cc: "boris@....io" <boris@....io>,
"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
"axboe@...nel.dk" <axboe@...nel.dk>,
Iverlin Wang (王苳霖) <Iverlin.Wang@...iatek.com>,
"josef@...icpanda.com" <josef@...icpanda.com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"matthias.bgg@...il.com" <matthias.bgg@...il.com>,
"angelogioacchino.delregno@...labora.com"
<angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH v3] blk-cgroup: Replace u64 sync with spinlock for iostat
update
On 7/17/24 12:55, tj@...nel.org wrote:
> Hello,
>
> Does something like the following work for you?
>
> Thanks.
>
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 37e6cc91d576..ec1d191f5c83 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -329,7 +329,6 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct gendisk *disk,
> INIT_WORK(&blkg->async_bio_work, blkg_async_bio_workfn);
> #endif
>
> - u64_stats_init(&blkg->iostat.sync);
> for_each_possible_cpu(cpu) {
> u64_stats_init(&per_cpu_ptr(blkg->iostat_cpu, cpu)->sync);
> per_cpu_ptr(blkg->iostat_cpu, cpu)->blkg = blkg;
> @@ -632,24 +631,26 @@ static void blkg_iostat_set(struct blkg_iostat *dst, struct blkg_iostat *src)
> static void __blkg_clear_stat(struct blkg_iostat_set *bis)
> {
> struct blkg_iostat cur = {0};
> - unsigned long flags;
>
> - flags = u64_stats_update_begin_irqsave(&bis->sync);
> blkg_iostat_set(&bis->cur, &cur);
> blkg_iostat_set(&bis->last, &cur);
> - u64_stats_update_end_irqrestore(&bis->sync, flags);
> }
>
> static void blkg_clear_stat(struct blkcg_gq *blkg)
> {
> + unsigned long flags;
> int cpu;
>
> + raw_spin_lock_irqsave(&blkg_stat_lock, flags);
> +
> for_each_possible_cpu(cpu) {
> struct blkg_iostat_set *s = per_cpu_ptr(blkg->iostat_cpu, cpu);
>
> __blkg_clear_stat(s);
> }
> __blkg_clear_stat(&blkg->iostat);
> +
> + raw_spin_unlock_irqrestore(&blkg_stat_lock, flags);
> }
>
> static int blkcg_reset_stats(struct cgroup_subsys_state *css,
> @@ -998,12 +999,10 @@ static void blkcg_iostat_update(struct blkcg_gq *blkg, struct blkg_iostat *cur,
> unsigned long flags;
>
> /* propagate percpu delta to global */
> - flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
> blkg_iostat_set(&delta, cur);
> blkg_iostat_sub(&delta, last);
> blkg_iostat_add(&blkg->iostat.cur, &delta);
> blkg_iostat_add(last, &delta);
> - u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
> }
>
> static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu)
> @@ -1134,9 +1133,9 @@ static void blkcg_fill_root_iostats(void)
> cpu_dkstats->sectors[STAT_DISCARD] << 9;
> }
>
> - flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
> + raw_spin_lock_irqsave(&blkg_stat_lock, flags);
> blkg_iostat_set(&blkg->iostat.cur, &tmp);
> - u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
> + raw_spin_unlock_irqrestore(&blkg_stat_lock, flags);
> }
> }
>
> @@ -1145,7 +1144,6 @@ static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s)
> struct blkg_iostat_set *bis = &blkg->iostat;
> u64 rbytes, wbytes, rios, wios, dbytes, dios;
> const char *dname;
> - unsigned seq;
> int i;
>
> if (!blkg->online)
> @@ -1157,16 +1155,14 @@ static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s)
>
> seq_printf(s, "%s ", dname);
>
> - do {
> - seq = u64_stats_fetch_begin(&bis->sync);
> -
> - rbytes = bis->cur.bytes[BLKG_IOSTAT_READ];
> - wbytes = bis->cur.bytes[BLKG_IOSTAT_WRITE];
> - dbytes = bis->cur.bytes[BLKG_IOSTAT_DISCARD];
> - rios = bis->cur.ios[BLKG_IOSTAT_READ];
> - wios = bis->cur.ios[BLKG_IOSTAT_WRITE];
> - dios = bis->cur.ios[BLKG_IOSTAT_DISCARD];
> - } while (u64_stats_fetch_retry(&bis->sync, seq));
> + raw_spin_lock_irq(&blkg_stat_lock);
> + rbytes = bis->cur.bytes[BLKG_IOSTAT_READ];
> + wbytes = bis->cur.bytes[BLKG_IOSTAT_WRITE];
> + dbytes = bis->cur.bytes[BLKG_IOSTAT_DISCARD];
> + rios = bis->cur.ios[BLKG_IOSTAT_READ];
> + wios = bis->cur.ios[BLKG_IOSTAT_WRITE];
> + dios = bis->cur.ios[BLKG_IOSTAT_DISCARD];
> + raw_spin_unlock_irq(&blkg_stat_lock, flags);
>
> if (rbytes || wbytes || rios || wios) {
> seq_printf(s, "rbytes=%llu wbytes=%llu rios=%llu wios=%llu dbytes=%llu dios=%llu",
>
bis->sync is still being used in blk_cgroup_bio_start(). Replacing it
with a global lock may kill performance. We may have to use a per-cpu
lock if we want to go this route of eliminating bis->sync.
Cheers,
Longman
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