@@ -170,6 +170,8 @@ struct throtl_data
unsigned long high_upgrade_time;
unsigned long high_downgrade_time;
+
+ unsigned int scale;
};
static void throtl_pending_timer_fn(unsigned long arg);
@@ -224,12 +226,27 @@ static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
static uint64_t tg_bps_limit(struct throtl_grp *tg, int rw)
{
struct blkcg_gq *blkg = tg_to_blkg(tg);
+ struct throtl_data *td;
uint64_t ret;
if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
return -1;
- ret = tg->bps[rw][tg->td->limit_index];
- if (ret == -1 && tg->td->limit_index == LIMIT_HIGH)
+ td = tg->td;
+ ret = tg->bps[rw][td->limit_index];
+ if (td->limit_index == LIMIT_MAX && tg->bps[rw][LIMIT_HIGH] != -1) {
+ uint64_t increase;
+
+ if (td->scale < 4096 && time_after_eq(jiffies,
+ td->high_upgrade_time + td->scale * td->throtl_slice)) {
+ unsigned int time = jiffies - td->high_upgrade_time;
+
+ td->scale = time / td->throtl_slice;
+ }
+ increase = (tg->bps[rw][LIMIT_HIGH] >> 1) * td->scale;
+ ret = min(tg->bps[rw][LIMIT_MAX],
+ tg->bps[rw][LIMIT_HIGH] + increase);
+ }
+ if (ret == -1 && td->limit_index == LIMIT_HIGH)
return tg->bps[rw][LIMIT_MAX];
return ret;
@@ -238,12 +255,28 @@ static uint64_t tg_bps_limit(struct throtl_grp *tg, int rw)
static unsigned int tg_iops_limit(struct throtl_grp *tg, int rw)
{
struct blkcg_gq *blkg = tg_to_blkg(tg);
+ struct throtl_data *td;
unsigned int ret;
if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
return -1;
- ret = tg->iops[rw][tg->td->limit_index];
- if (ret == -1 && tg->td->limit_index == LIMIT_HIGH)
+ td = tg->td;
+ ret = tg->iops[rw][td->limit_index];
+ if (td->limit_index == LIMIT_MAX && tg->iops[rw][LIMIT_HIGH] != -1) {
+ uint64_t increase;
+
+ if (td->scale < 4096 && time_after_eq(jiffies,
+ td->high_upgrade_time + td->scale * td->throtl_slice)) {
+ unsigned int time = jiffies - td->high_upgrade_time;
+
+ td->scale = time / td->throtl_slice;
+ }
+
+ increase = (tg->iops[rw][LIMIT_HIGH] >> 1) * td->scale;
+ ret = min(tg->iops[rw][LIMIT_MAX],
+ tg->iops[rw][LIMIT_HIGH] + (unsigned int)increase);
+ }
+ if (ret == -1 && td->limit_index == LIMIT_HIGH)
return tg->iops[rw][LIMIT_MAX];
return ret;
}
@@ -1676,6 +1709,7 @@ static void throtl_upgrade_state(struct throtl_data *td)
td->limit_index = LIMIT_MAX;
td->high_upgrade_time = jiffies;
+ td->scale = 0;
rcu_read_lock();
blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
struct throtl_grp *tg = blkg_to_tg(blkg);
When cgroups all reach high limit, cgroups can dispatch more IO. This could make some cgroups dispatch more IO but others not, and even some cgroups could dispatch less IO than their high limit. For example, cg1 high limit 10MB/s, cg2 limit 80MB/s, assume disk maximum bandwidth is 120M/s for the workload. Their bps could something like this: cg1/cg2 bps: T1: 10/80 -> T2: 60/60 -> T3: 10/80 At T1, all cgroups reach high limit, so they can dispatch more IO later. Then cg1 dispatch more IO and cg2 has no room to dispatch enough IO. At T2, cg2 only dispatches 60M/s. Since We detect cg2 dispatches less IO than its high limit 80M/s, we downgrade the queue from LIMIT_MAX to LIMIT_HIGH, then all cgroups are throttled to their high limit (T3). cg2 will have bandwidth below its high limit at most time. The big problem here is we don't know the maximum bandwidth of the workload, so we can't make smart decision to avoid the situation. This patch makes cgroup bandwidth change smooth. After disk upgrades from LIMIT_HIGH to LIMIT_MAX, we don't allow cgroups use all bandwidth upto their max limit immediately. Their bandwidth limit will be increased gradually to avoid above situation. So above example will became something like: cg1/cg2 bps: 10/80 -> 15/105 -> 20/100 -> 25/95 -> 30/90 -> 35/85 -> 40/80 -> 45/75 -> 10/80 In this way cgroups bandwidth will be above their limit in majority time, this still doesn't fully utilize disk bandwidth, but that's something we pay for sharing. Note this doesn't completely avoid cgroup running under its high limit. The best way to guarantee cgroup doesn't run under its limit is to set max limit. For example, if we set cg1 max limit to 40, cg2 will never run under its high limit. Signed-off-by: Shaohua Li <shli@fb.com> --- block/blk-throttle.c | 42 ++++++++++++++++++++++++++++++++++++++---- 1 file changed, 38 insertions(+), 4 deletions(-)