On Tue, Sep 01, 2020 at 02:52:33PM -0400, Tejun Heo wrote:
> blk-iocost has been reading percpu stat counters from remote cpus which on
> some archs can lead to torn reads in really rare occassions. Use local[64]_t
> for those counters.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> ---
> block/blk-iocost.c | 37 +++++++++++++++++++++++++++----------
> 1 file changed, 27 insertions(+), 10 deletions(-)
>
> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> index d37b55db2409..e2266e7692b4 100644
> --- a/block/blk-iocost.c
> +++ b/block/blk-iocost.c
> @@ -179,6 +179,8 @@
> #include <linux/parser.h>
> #include <linux/sched/signal.h>
> #include <linux/blk-cgroup.h>
> +#include <asm/local.h>
> +#include <asm/local64.h>
Hi Tejun,
FYI, I am just noticing this but this breaks my allyesconfig build
on OpenRISC; as 32-bit arch/openrisc doesn't define local64.h
In general local64 is slow on 32-bit architectures, would that
be a problem with the usage here? Are the calls to local64_*
below on critical paths?
Either way I will submit a patch in include generic local64.h
on OpenRISC, I confirmed it fixes the build. I do not know of anyone
using cgroups on OpenRISC systems.
-Stafford
> #include "blk-rq-qos.h"
> #include "blk-stat.h"
> #include "blk-wbt.h"
> @@ -373,8 +375,8 @@ struct ioc_params {
> };
>
> struct ioc_missed {
> - u32 nr_met;
> - u32 nr_missed;
> + local_t nr_met;
> + local_t nr_missed;
> u32 last_met;
> u32 last_missed;
> };
> @@ -382,7 +384,7 @@ struct ioc_missed {
> struct ioc_pcpu_stat {
> struct ioc_missed missed[2];
>
> - u64 rq_wait_ns;
> + local64_t rq_wait_ns;
> u64 last_rq_wait_ns;
> };
>
> @@ -1278,8 +1280,8 @@ static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p
> u64 this_rq_wait_ns;
>
> for (rw = READ; rw <= WRITE; rw++) {
> - u32 this_met = READ_ONCE(stat->missed[rw].nr_met);
> - u32 this_missed = READ_ONCE(stat->missed[rw].nr_missed);
> + u32 this_met = local_read(&stat->missed[rw].nr_met);
> + u32 this_missed = local_read(&stat->missed[rw].nr_missed);
>
> nr_met[rw] += this_met - stat->missed[rw].last_met;
> nr_missed[rw] += this_missed - stat->missed[rw].last_missed;
> @@ -1287,7 +1289,7 @@ static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p
> stat->missed[rw].last_missed = this_missed;
> }
>
> - this_rq_wait_ns = READ_ONCE(stat->rq_wait_ns);
> + this_rq_wait_ns = local64_read(&stat->rq_wait_ns);
> rq_wait_ns += this_rq_wait_ns - stat->last_rq_wait_ns;
> stat->last_rq_wait_ns = this_rq_wait_ns;
> }
> @@ -1908,6 +1910,7 @@ static void ioc_rqos_done_bio(struct rq_qos *rqos, struct bio *bio)
> static void ioc_rqos_done(struct rq_qos *rqos, struct request *rq)
> {
> struct ioc *ioc = rqos_to_ioc(rqos);
> + struct ioc_pcpu_stat *ccs;
> u64 on_q_ns, rq_wait_ns, size_nsec;
> int pidx, rw;
>
> @@ -1931,13 +1934,17 @@ static void ioc_rqos_done(struct rq_qos *rqos, struct request *rq)
> rq_wait_ns = rq->start_time_ns - rq->alloc_time_ns;
> size_nsec = div64_u64(calc_size_vtime_cost(rq, ioc), VTIME_PER_NSEC);
>
> + ccs = get_cpu_ptr(ioc->pcpu_stat);
> +
> if (on_q_ns <= size_nsec ||
> on_q_ns - size_nsec <= ioc->params.qos[pidx] * NSEC_PER_USEC)
> - this_cpu_inc(ioc->pcpu_stat->missed[rw].nr_met);
> + local_inc(&ccs->missed[rw].nr_met);
> else
> - this_cpu_inc(ioc->pcpu_stat->missed[rw].nr_missed);
> + local_inc(&ccs->missed[rw].nr_missed);
> +
> + local64_add(rq_wait_ns, &ccs->rq_wait_ns);
>
> - this_cpu_add(ioc->pcpu_stat->rq_wait_ns, rq_wait_ns);
> + put_cpu_ptr(ccs);
> }
>
> static void ioc_rqos_queue_depth_changed(struct rq_qos *rqos)
> @@ -1977,7 +1984,7 @@ static int blk_iocost_init(struct request_queue *q)
> {
> struct ioc *ioc;
> struct rq_qos *rqos;
> - int ret;
> + int i, cpu, ret;
>
> ioc = kzalloc(sizeof(*ioc), GFP_KERNEL);
> if (!ioc)
> @@ -1989,6 +1996,16 @@ static int blk_iocost_init(struct request_queue *q)
> return -ENOMEM;
> }
>
> + for_each_possible_cpu(cpu) {
> + struct ioc_pcpu_stat *ccs = per_cpu_ptr(ioc->pcpu_stat, cpu);
> +
> + for (i = 0; i < ARRAY_SIZE(ccs->missed); i++) {
> + local_set(&ccs->missed[i].nr_met, 0);
> + local_set(&ccs->missed[i].nr_missed, 0);
> + }
> + local64_set(&ccs->rq_wait_ns, 0);
> + }
> +
> rqos = &ioc->rqos;
> rqos->id = RQ_QOS_COST;
> rqos->ops = &ioc_rqos_ops;
> --
> 2.26.2
>
