From: Jialin Wang <wjl.linux@gmail.com> mainline inclusion from mainline-v7.1-rc1 commit f91ffe89b2016d280995a9c28d73288b02d83615 category: bugfix bugzilla: https://atomgit.com/openeuler/kernel/issues/9104 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- When a disk is saturated, it is common for no IOs to complete within a timer period. Currently, in this case, rq_wait_pct and missed_ppm are calculated as 0, the iocost incorrectly interprets this as meeting QoS targets and resets busy_level to 0. This reset prevents busy_level from reaching the threshold (4) needed to reduce vrate. On certain cloud storage, such as Azure Premium SSD, we observed that iocost may fail to reduce vrate for tens of seconds during saturation, failing to mitigate noisy neighbor issues. Fix this by tracking the number of IO completions (nr_done) in a period. If nr_done is 0 and there are lagging IOs, the saturation status is unknown, so we keep busy_level unchanged. The issue is consistently reproducible on Azure Standard_D8as_v5 (Dasv5) VMs with 512GB Premium SSD (P20) using the script below. It was not observed on GCP n2d VMs (with 100G pd-ssd and 1.5T local-ssd), and no regressions were found with this patch. In this script, cgA performs large IOs with iodepth=128, while cgB performs small IOs with iodepth=1 rate_iops=100 rw=randrw. With iocost enabled, we expect it to throttle cgA, the submission latency (slat) of cgA should be significantly higher, cgB can reach 200 IOPS and the completion latency (clat) should below. BLK_DEVID="8:0" MODEL="rbps=173471131 rseqiops=3566 rrandiops=3566 wbps=173333269 wseqiops=3566 wrandiops=3566" QOS="rpct=90 rlat=3500 wpct=90 wlat=3500 min=80 max=10000" echo "$BLK_DEVID ctrl=user model=linear $MODEL" > /sys/fs/cgroup/io.cost.model echo "$BLK_DEVID enable=1 ctrl=user $QOS" > /sys/fs/cgroup/io.cost.qos CG_A="/sys/fs/cgroup/cgA" CG_B="/sys/fs/cgroup/cgB" FILE_A="/path/to/sda/A.fio.testfile" FILE_B="/path/to/sda/B.fio.testfile" RESULT_DIR="./iocost_results_$(date +%Y%m%d_%H%M%S)" mkdir -p "$CG_A" "$CG_B" "$RESULT_DIR" get_result() { local file=$1 local label=$2 local results=$(jq -r ' .jobs[0].mixed | ( .iops | tonumber | round ) as $iops | ( .bw_bytes / 1024 / 1024 ) as $bps | ( .slat_ns.mean / 1000000 ) as $slat | ( .clat_ns.mean / 1000000 ) as $avg | ( .clat_ns.max / 1000000 ) as $max | ( .clat_ns.percentile["90.000000"] / 1000000 ) as $p90 | ( .clat_ns.percentile["99.000000"] / 1000000 ) as $p99 | ( .clat_ns.percentile["99.900000"] / 1000000 ) as $p999 | ( .clat_ns.percentile["99.990000"] / 1000000 ) as $p9999 | "\($iops)|\($bps)|\($slat)|\($avg)|\($max)|\($p90)|\($p99)|\($p999)|\($p9999)" ' "$file") IFS='|' read -r iops bps slat avg max p90 p99 p999 p9999 <<<"$results" printf "%-8s %-6s %-7.2f %-8.2f %-8.2f %-8.2f %-8.2f %-8.2f %-8.2f %-8.2f\n" \ "$label" "$iops" "$bps" "$slat" "$avg" "$max" "$p90" "$p99" "$p999" "$p9999" } run_fio() { local cg_path=$1 local filename=$2 local name=$3 local bs=$4 local qd=$5 local out=$6 shift 6 local extra=$@ ( pid=$(sh -c 'echo $PPID') echo $pid >"${cg_path}/cgroup.procs" fio --name="$name" --filename="$filename" --direct=1 --rw=randrw --rwmixread=50 \ --ioengine=libaio --bs="$bs" --iodepth="$qd" --size=4G --runtime=10 \ --time_based --group_reporting --unified_rw_reporting=mixed \ --output-format=json --output="$out" $extra >/dev/null 2>&1 ) & } echo "Starting Test ..." for bs_b in "4k" "32k" "256k"; do echo "Running iteration: BS=$bs_b" out_a="${RESULT_DIR}/cgA_1m.json" out_b="${RESULT_DIR}/cgB_${bs_b}.json" # cgA: Heavy background (BS 1MB, QD 128) run_fio "$CG_A" "$FILE_A" "cgA" "1m" 128 "$out_a" # cgB: Latency sensitive (Variable BS, QD 1, Read/Write IOPS limit 100) run_fio "$CG_B" "$FILE_B" "cgB" "$bs_b" 1 "$out_b" "--rate_iops=100" wait SUMMARY_DATA+="$(get_result "$out_a" "cgA-1m")"$'\n' SUMMARY_DATA+="$(get_result "$out_b" "cgB-$bs_b")"$'\n\n' done echo -e "\nFinal Results Summary:\n" printf "%-8s %-6s %-7s %-8s %-8s %-8s %-8s %-8s %-8s %-8s\n" \ "" "" "" "slat" "clat" "clat" "clat" "clat" "clat" "clat" printf "%-8s %-6s %-7s %-8s %-8s %-8s %-8s %-8s %-8s %-8s\n\n" \ "CGROUP" "IOPS" "MB/s" "avg(ms)" "avg(ms)" "max(ms)" "P90(ms)" "P99" "P99.9" "P99.99" echo "$SUMMARY_DATA" echo "Results saved in $RESULT_DIR" Before: slat clat clat clat clat clat clat CGROUP IOPS MB/s avg(ms) avg(ms) max(ms) P90(ms) P99 P99.9 P99.99 cgA-1m 166 166.37 3.44 748.95 1298.29 977.27 1233.13 1300.23 1300.23 cgB-4k 5 0.02 0.02 181.74 761.32 742.39 759.17 759.17 759.17 cgA-1m 167 166.51 1.98 748.68 1549.41 809.50 1451.23 1551.89 1551.89 cgB-32k 6 0.18 0.02 169.98 761.76 742.39 759.17 759.17 759.17 cgA-1m 166 165.55 2.89 750.89 1540.37 851.44 1451.23 1535.12 1535.12 cgB-256k 5 1.30 0.02 191.35 759.51 750.78 759.17 759.17 759.17 After: slat clat clat clat clat clat clat CGROUP IOPS MB/s avg(ms) avg(ms) max(ms) P90(ms) P99 P99.9 P99.99 cgA-1m 162 162.48 6.14 749.69 850.02 826.28 834.67 843.06 851.44 cgB-4k 199 0.78 0.01 1.95 42.12 2.57 7.50 34.87 42.21 cgA-1m 146 146.20 6.83 833.04 908.68 893.39 901.78 910.16 910.16 cgB-32k 200 6.25 0.01 2.32 31.40 3.06 7.50 16.58 31.33 cgA-1m 110 110.46 9.04 1082.67 1197.91 1182.79 1199.57 1199.57 1199.57 cgB-256k 200 49.98 0.02 3.69 22.20 4.88 9.11 20.05 22.15 Signed-off-by: Jialin Wang <wjl.linux@gmail.com> Acked-by: Tejun Heo <tj@kernel.org> Link: https://patch.msgid.link/20260331100509.182882-1-wjl.linux@gmail.com Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Zizhi Wo <wozizhi@huawei.com> --- block/blk-iocost.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/block/blk-iocost.c b/block/blk-iocost.c index 0019b67aed15..133d3f5828ee 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -1595,11 +1595,12 @@ static enum hrtimer_restart iocg_waitq_timer_fn(struct hrtimer *timer) iocg_unlock(iocg, pay_debt, &flags); return HRTIMER_NORESTART; } -static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p) +static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p, + u32 *nr_done) { u32 nr_met[2] = { }; u32 nr_missed[2] = { }; u64 rq_wait_ns = 0; int cpu, rw; @@ -1632,10 +1633,12 @@ static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p missed_ppm_ar[rw] = 0; } *rq_wait_pct_p = div64_u64(rq_wait_ns * 100, ioc->period_us * NSEC_PER_USEC); + + *nr_done = nr_met[READ] + nr_met[WRITE] + nr_missed[READ] + nr_missed[WRITE]; } /* was iocg idle this period? */ static bool iocg_is_idle(struct ioc_gq *iocg) { @@ -2249,16 +2252,16 @@ static void ioc_timer_fn(struct timer_list *timer) LIST_HEAD(surpluses); int nr_debtors, nr_shortages = 0, nr_lagging = 0; u64 usage_us_sum = 0; u32 ppm_rthr; u32 ppm_wthr; - u32 missed_ppm[2], rq_wait_pct; + u32 missed_ppm[2], rq_wait_pct, nr_done; u64 period_vtime; int prev_busy_level; /* how were the latencies during the period? */ - ioc_lat_stat(ioc, missed_ppm, &rq_wait_pct); + ioc_lat_stat(ioc, missed_ppm, &rq_wait_pct, &nr_done); /* take care of active iocgs */ spin_lock_irq(&ioc->lock); ppm_rthr = MILLION - ioc->params.qos[QOS_RPPM]; @@ -2396,13 +2399,21 @@ static void ioc_timer_fn(struct timer_list *timer) * too much IO and should lower vtime rate. If we're not missing * and experiencing shortages but not surpluses, we're too stingy * and should increase vtime rate. */ prev_busy_level = ioc->busy_level; - if (rq_wait_pct > RQ_WAIT_BUSY_PCT || - missed_ppm[READ] > ppm_rthr || - missed_ppm[WRITE] > ppm_wthr) { + if (!nr_done && nr_lagging) { + /* + * When there are lagging IOs but no completions, we don't + * know if the IO latency will meet the QoS targets. The + * disk might be saturated or not. We should not reset + * busy_level to 0 (which would prevent vrate from scaling + * up or down), but rather to keep it unchanged. + */ + } else if (rq_wait_pct > RQ_WAIT_BUSY_PCT || + missed_ppm[READ] > ppm_rthr || + missed_ppm[WRITE] > ppm_wthr) { /* clearly missing QoS targets, slow down vrate */ ioc->busy_level = max(ioc->busy_level, 0); ioc->busy_level++; } else if (rq_wait_pct <= RQ_WAIT_BUSY_PCT * UNBUSY_THR_PCT / 100 && missed_ppm[READ] <= ppm_rthr * UNBUSY_THR_PCT / 100 && -- 2.52.0