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Subject[RFC PATCH] blk-throttle: add burst allowance.
Date
Allows configuration additional bytes or ios before a throttle is
triggered.

This allows implementation of a bucket style rate-limit/throttle on a
block device. Previously, bursting to a device was limited to allowance
granted in a single throtl_slice (similar to a bucket with limit N and
refill rate N/slice).

Additional parameters bytes/io_burst_conf defined for tg, which define a
number of bytes/ios that must be depleted before throttling happens. A
tg that does not deplete this allowance functions as though it has no
configured limits. tgs earn additional allowance at rate defined by
bps/iops for the tg. Once a tg has *_disp > *_burst_conf, throttling
kicks in. If a tg is idle for a while, it will again have some burst
allowance before it gets throttled again.

slice_end for a tg is extended until io_disp/byte_disp would fall to 0,
when all "used" burst allowance would be earned back. trim_slice still
does progress slice_start as before and decrements *_disp as before, and
tgs continue to get bytes/ios in throtl_slice intervals.

Signed-off-by: Khazhismel Kumykov <khazhy@google.com>
---
block/Kconfig | 11 +++
block/blk-throttle.c | 192 +++++++++++++++++++++++++++++++++++++++++++++++----
2 files changed, 189 insertions(+), 14 deletions(-)

diff --git a/block/Kconfig b/block/Kconfig
index 28ec55752b68..fbd05b419f93 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -128,6 +128,17 @@ config BLK_DEV_THROTTLING_LOW

Note, this is an experimental interface and could be changed someday.

+config BLK_DEV_THROTTLING_BURST
+ bool "Block throttling .burst allowance interface"
+ depends on BLK_DEV_THROTTLING
+ default n
+ ---help---
+ Add .burst allowance for block throttling. Burst allowance allows for
+ additional unthrottled usage, while still limiting speed for sustained
+ usage.
+
+ If in doubt, say N.
+
config BLK_CMDLINE_PARSER
bool "Block device command line partition parser"
default n
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 96ad32623427..27c084312772 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -157,6 +157,11 @@ struct throtl_grp {
/* Number of bio's dispatched in current slice */
unsigned int io_disp[2];

+#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
+ uint64_t bytes_burst_conf[2];
+ unsigned int io_burst_conf[2];
+#endif
+
unsigned long last_low_overflow_time[2];

uint64_t last_bytes_disp[2];
@@ -507,6 +512,12 @@ static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
tg->bps_conf[WRITE][LIMIT_MAX] = U64_MAX;
tg->iops_conf[READ][LIMIT_MAX] = UINT_MAX;
tg->iops_conf[WRITE][LIMIT_MAX] = UINT_MAX;
+#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
+ tg->bytes_burst_conf[READ] = 0;
+ tg->bytes_burst_conf[WRITE] = 0;
+ tg->io_burst_conf[READ] = 0;
+ tg->io_burst_conf[WRITE] = 0;
+#endif
/* LIMIT_LOW will have default value 0 */

tg->latency_target = DFL_LATENCY_TARGET;
@@ -800,6 +811,26 @@ static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw)
tg->slice_end[rw], jiffies);
}

+/*
+ * When current slice should end.
+ *
+ * With CONFIG_BLK_DEV_THROTTLING_BURST, we will wait longer than min_wait
+ * for slice to recover used burst allowance. (*_disp -> 0). Setting slice_end
+ * before this would result in tg receiving additional burst allowance.
+ */
+static inline unsigned long throtl_slice_wait(struct throtl_grp *tg, bool rw,
+ unsigned long min_wait)
+{
+ unsigned long bytes_wait = 0, io_wait = 0;
+#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
+ if (tg->bytes_burst_conf[rw])
+ bytes_wait = (tg->bytes_disp[rw] * HZ) / tg_bps_limit(tg, rw);
+ if (tg->io_burst_conf[rw])
+ io_wait = (tg->io_disp[rw] * HZ) / tg_iops_limit(tg, rw);
+#endif
+ return max(min_wait, max(bytes_wait, io_wait));
+}
+
static inline void throtl_set_slice_end(struct throtl_grp *tg, bool rw,
unsigned long jiffy_end)
{
@@ -849,7 +880,8 @@ static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
* is bad because it does not allow new slice to start.
*/

- throtl_set_slice_end(tg, rw, jiffies + tg->td->throtl_slice);
+ throtl_set_slice_end(tg, rw,
+ jiffies + throtl_slice_wait(tg, rw, tg->td->throtl_slice));

time_elapsed = jiffies - tg->slice_start[rw];

@@ -889,7 +921,7 @@ static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
unsigned long *wait)
{
bool rw = bio_data_dir(bio);
- unsigned int io_allowed;
+ unsigned int io_allowed, io_disp;
unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
u64 tmp;

@@ -908,6 +940,17 @@ static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
* have been trimmed.
*/

+ io_disp = tg->io_disp[rw];
+
+#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
+ if (tg->io_disp[rw] < tg->io_burst_conf[rw]) {
+ if (wait)
+ *wait = 0;
+ return true;
+ }
+ io_disp -= tg->io_burst_conf[rw];
+#endif
+
tmp = (u64)tg_iops_limit(tg, rw) * jiffy_elapsed_rnd;
do_div(tmp, HZ);

@@ -916,14 +959,14 @@ static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
else
io_allowed = tmp;

- if (tg->io_disp[rw] + 1 <= io_allowed) {
+ if (io_disp + 1 <= io_allowed) {
if (wait)
*wait = 0;
return true;
}

/* Calc approx time to dispatch */
- jiffy_wait = ((tg->io_disp[rw] + 1) * HZ) / tg_iops_limit(tg, rw) + 1;
+ jiffy_wait = ((io_disp + 1) * HZ) / tg_iops_limit(tg, rw) + 1;

if (jiffy_wait > jiffy_elapsed)
jiffy_wait = jiffy_wait - jiffy_elapsed;
@@ -939,7 +982,7 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
unsigned long *wait)
{
bool rw = bio_data_dir(bio);
- u64 bytes_allowed, extra_bytes, tmp;
+ u64 bytes_allowed, extra_bytes, bytes_disp, tmp;
unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
unsigned int bio_size = throtl_bio_data_size(bio);

@@ -951,18 +994,28 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,

jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);

+ bytes_disp = tg->bytes_disp[rw];
+#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
+ if (tg->bytes_disp[rw] < tg->bytes_burst_conf[rw]) {
+ if (wait)
+ *wait = 0;
+ return true;
+ }
+ bytes_disp -= tg->bytes_burst_conf[rw];
+#endif
+
tmp = tg_bps_limit(tg, rw) * jiffy_elapsed_rnd;
do_div(tmp, HZ);
bytes_allowed = tmp;

- if (tg->bytes_disp[rw] + bio_size <= bytes_allowed) {
+ if (bytes_disp + bio_size <= bytes_allowed) {
if (wait)
*wait = 0;
return true;
}

/* Calc approx time to dispatch */
- extra_bytes = tg->bytes_disp[rw] + bio_size - bytes_allowed;
+ extra_bytes = bytes_disp + bio_size - bytes_allowed;
jiffy_wait = div64_u64(extra_bytes * HZ, tg_bps_limit(tg, rw));

if (!jiffy_wait)
@@ -986,7 +1039,7 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
unsigned long *wait)
{
bool rw = bio_data_dir(bio);
- unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
+ unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0, disp_time;

/*
* Currently whole state machine of group depends on first bio
@@ -1015,10 +1068,10 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
if (throtl_slice_used(tg, rw) && !(tg->service_queue.nr_queued[rw]))
throtl_start_new_slice(tg, rw);
else {
- if (time_before(tg->slice_end[rw],
- jiffies + tg->td->throtl_slice))
- throtl_extend_slice(tg, rw,
- jiffies + tg->td->throtl_slice);
+ disp_time = jiffies + throtl_slice_wait(
+ tg, rw, tg->td->throtl_slice);
+ if (time_before(tg->slice_end[rw], disp_time))
+ throtl_extend_slice(tg, rw, disp_time);
}

if (tg_with_in_bps_limit(tg, bio, &bps_wait) &&
@@ -1033,8 +1086,9 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
if (wait)
*wait = max_wait;

- if (time_before(tg->slice_end[rw], jiffies + max_wait))
- throtl_extend_slice(tg, rw, jiffies + max_wait);
+ disp_time = jiffies + throtl_slice_wait(tg, rw, max_wait);
+ if (time_before(tg->slice_end[rw], disp_time))
+ throtl_extend_slice(tg, rw, disp_time);

return 0;
}
@@ -1705,6 +1759,108 @@ static ssize_t tg_set_limit(struct kernfs_open_file *of,
return ret ?: nbytes;
}

+#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
+static u64 tg_prfill_burst(struct seq_file *sf, struct blkg_policy_data *pd,
+ int data)
+{
+ struct throtl_grp *tg = pd_to_tg(pd);
+ const char *dname = blkg_dev_name(pd->blkg);
+ char bufs[4][21];
+
+ if (!dname)
+ return 0;
+
+ if (tg->bytes_burst_conf[READ] == 0 &&
+ tg->bytes_burst_conf[WRITE] == 0 &&
+ tg->io_burst_conf[READ] == 0 &&
+ tg->io_burst_conf[WRITE] == 0)
+ return 0;
+
+ snprintf(bufs[0], sizeof(bufs[0]), "%llu",
+ tg->bytes_burst_conf[READ]);
+ snprintf(bufs[1], sizeof(bufs[1]), "%llu",
+ tg->bytes_burst_conf[WRITE]);
+ snprintf(bufs[2], sizeof(bufs[2]), "%u",
+ tg->io_burst_conf[READ]);
+ snprintf(bufs[3], sizeof(bufs[3]), "%u",
+ tg->io_burst_conf[WRITE]);
+
+ seq_printf(sf, "%s brbyte=%s bwbyte=%s brio=%s bwio=%s\n",
+ dname, bufs[0], bufs[1], bufs[2], bufs[3]);
+ return 0;
+}
+
+static int tg_print_burst(struct seq_file *sf, void *v)
+{
+ blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_burst,
+ &blkcg_policy_throtl, 0, false);
+ return 0;
+}
+
+static ssize_t tg_set_burst(struct kernfs_open_file *of,
+ char *buf, size_t nbytes, loff_t off)
+{
+ struct blkcg *blkcg = css_to_blkcg(of_css(of));
+ struct blkg_conf_ctx ctx;
+ struct throtl_grp *tg;
+ u64 v[4];
+ int ret;
+
+ ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
+ if (ret)
+ return ret;
+
+ tg = blkg_to_tg(ctx.blkg);
+
+ v[0] = tg->bytes_burst_conf[READ];
+ v[1] = tg->bytes_burst_conf[WRITE];
+ v[2] = tg->io_burst_conf[READ];
+ v[3] = tg->io_burst_conf[WRITE];
+
+ while (true) {
+ char tok[28]; /* bwbyte=18446744073709551616 */
+ char *p;
+ u64 val = U64_MAX;
+ int len;
+
+ if (sscanf(ctx.body, "%27s%n", tok, &len) != 1)
+ break;
+ if (tok[0] == '\0')
+ break;
+ ctx.body += len;
+
+ ret = -EINVAL;
+ p = tok;
+ strsep(&p, "=");
+ if (!p || (kstrtoull(p, 0, &val) != 0 && strcmp(p, "max")))
+ goto out_finish;
+
+ ret = -EINVAL;
+ if (!strcmp(tok, "brbyte"))
+ v[0] = val;
+ else if (!strcmp(tok, "bwbyte"))
+ v[1] = val;
+ else if (!strcmp(tok, "brio"))
+ v[2] = min_t(u64, val, UINT_MAX);
+ else if (!strcmp(tok, "bwio"))
+ v[3] = min_t(u64, val, UINT_MAX);
+ else
+ goto out_finish;
+ }
+
+ tg->bytes_burst_conf[READ] = v[0];
+ tg->bytes_burst_conf[WRITE] = v[1];
+ tg->io_burst_conf[READ] = v[2];
+ tg->io_burst_conf[WRITE] = v[3];
+
+ tg_conf_updated(tg, false);
+ ret = 0;
+out_finish:
+ blkg_conf_finish(&ctx);
+ return ret ?: nbytes;
+}
+#endif
+
static struct cftype throtl_files[] = {
#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
{
@@ -1714,6 +1870,14 @@ static struct cftype throtl_files[] = {
.write = tg_set_limit,
.private = LIMIT_LOW,
},
+#endif
+#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
+ {
+ .name = "burst",
+ .flags = CFTYPE_NOT_ON_ROOT,
+ .seq_show = tg_print_burst,
+ .write = tg_set_burst,
+ },
#endif
{
.name = "max",
--
2.15.0.448.gf294e3d99a-goog
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