Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit da87591b authored by Kai-Heng Feng's avatar Kai-Heng Feng Committed by Christoph Hellwig
Browse files

nvme: only consider exit latency when choosing useful non-op power states 



When a NVMe is in non-op states, the latency is exlat.
The latency will be enlat + exlat only when the NVMe tries to transit
from operational state right atfer it begins to transit to
non-operational state, which should be a rare case.

Therefore, as Andy Lutomirski suggests, use exlat only when deciding power
states to trainsit to.

Signed-off-by: default avatarKai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
parent 24b7f059

drivers/nvme/host/core.c

+9 −6
Original line number Diff line number Diff line
@@ -1342,7 +1342,7 @@ static void nvme_configure_apst(struct nvme_ctrl *ctrl) 
	 * transitioning between power states.  Therefore, when running

	 * in any given state, we will enter the next lower-power

	 * non-operational state after waiting 50 * (enlat + exlat)

	 * microseconds, as long as that state's total latency is under

	 * microseconds, as long as that state's exit latency is under

	 * the requested maximum latency.

	 *

	 * We will not autonomously enter any non-operational state for
@@ -1387,7 +1387,7 @@ static void nvme_configure_apst(struct nvme_ctrl *ctrl) 
		 * lowest-power state, not the number of states.

		 */

		for (state = (int)ctrl->npss; state >= 0; state--) {

			u64 total_latency_us, transition_ms;

			u64 total_latency_us, exit_latency_us, transition_ms;



			if (target)

				table->entries[state] = target;
@@ -1408,12 +1408,15 @@ static void nvme_configure_apst(struct nvme_ctrl *ctrl) 
			      NVME_PS_FLAGS_NON_OP_STATE))

				continue;



			total_latency_us =

				(u64)le32_to_cpu(ctrl->psd[state].entry_lat) +

				+ le32_to_cpu(ctrl->psd[state].exit_lat);

			if (total_latency_us > ctrl->ps_max_latency_us)

			exit_latency_us =

				(u64)le32_to_cpu(ctrl->psd[state].exit_lat);

			if (exit_latency_us > ctrl->ps_max_latency_us)

				continue;



			total_latency_us =

				exit_latency_us +

				le32_to_cpu(ctrl->psd[state].entry_lat);



			/*

			 * This state is good.  Use it as the APST idle

			 * target for higher power states.