| Message ID | 20240930201307.330692-3-mschmidt@redhat.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 6cd695706f8bb3d06a4dda1f7d673dbfcca45784 |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | qed: 'ethtool -d' faster, less latency | expand |
diff --git a/drivers/net/ethernet/qlogic/qed/qed_debug.c b/drivers/net/ethernet/qlogic/qed/qed_debug.c index f67be4b8ad43..464a72afb758 100644 --- a/drivers/net/ethernet/qlogic/qed/qed_debug.c +++ b/drivers/net/ethernet/qlogic/qed/qed_debug.c @@ -2873,6 +2873,7 @@ static u32 qed_grc_dump_ctx_data(struct qed_hwfn *p_hwfn, false, SPLIT_TYPE_NONE, 0); } + cond_resched(); } return offset;
On a kernel with preemption none or voluntary, 'ethtool -d' on a qede network device can cause a big latency spike. The biggest part of it is the loop in qed_grc_dump_ctx_data. The function is called only from the .get_size and .perform_dump callbacks for the "grc" feature defined in qed_features_lookup[]. As far as I can see, they are used in: - qed's devlink healh reporter .dump op - qede's ethtool get_regs/get_regs_len/get_dump_data ops - qedf's qedf_get_grc_dump, called from: - qedf_sysfs_write_grcdump - "grcdump" sysfs attribute write - qedf_wq_grcdump - a workqueue It is safe to sleep in all of them. Let's insert a cond_resched() in the outer loop to let other tasks run. Measured using this script: #!/bin/bash DEV=ens3f1 echo wakeup_rt > /sys/kernel/tracing/current_tracer echo 0 > /sys/kernel/tracing/tracing_max_latency echo 1 > /sys/kernel/tracing/tracing_on echo "Setting the task CPU affinity" taskset -p 1 $$ > /dev/null echo "Starting the real-time task" chrt -f 50 bash -c 'while sleep 0.01; do :; done' & sleep 1 echo "Running: ethtool -d $DEV" time ethtool -d $DEV > /dev/null kill %1 echo 0 > /sys/kernel/tracing/tracing_on echo "Measured latency: $(</sys/kernel/tracing/tracing_max_latency) us" echo "To see the latency trace: less /sys/kernel/tracing/trace" The patch lowers the latency from 180 ms to 53 ms on my test system with voluntary preemption. Signed-off-by: Michal Schmidt <mschmidt@redhat.com> --- drivers/net/ethernet/qlogic/qed/qed_debug.c | 1 + 1 file changed, 1 insertion(+)