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Date:   Fri, 28 Feb 2020 18:52:28 -0800
From:   Josh Triplett <josh@joshtriplett.org>
To:     Keith Busch <kbusch@kernel.org>, Jens Axboe <axboe@fb.com>,
        Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>
Cc:     linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: [PATCH] nvme: Check for readiness more quickly, to speed up boot time
Message-ID: <20200229025228.GA203607@localhost>
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After initialization, nvme_wait_ready checks for readiness every 100ms,
even though the drive may be ready far sooner than that. This delays
system boot by hundreds of milliseconds. Reduce the delay, checking for
readiness every millisecond instead.

Boot-time tests on an AWS c5.12xlarge:

Before:
[    0.546936] initcall nvme_init+0x0/0x5b returned 0 after 37 usecs
...
[    0.764178] nvme nvme0: 2/0/0 default/read/poll queues
[    0.768424]  nvme0n1: p1
[    0.774132] EXT4-fs (nvme0n1p1): mounted filesystem with ordered data mode. Opts: (null)
[    0.774146] VFS: Mounted root (ext4 filesystem) on device 259:1.
...
[    0.788141] Run /sbin/init as init process

After:
[    0.537088] initcall nvme_init+0x0/0x5b returned 0 after 37 usecs
...
[    0.543457] nvme nvme0: 2/0/0 default/read/poll queues
[    0.548473]  nvme0n1: p1
[    0.554339] EXT4-fs (nvme0n1p1): mounted filesystem with ordered data mode. Opts: (null)
[    0.554344] VFS: Mounted root (ext4 filesystem) on device 259:1.
...
[    0.567931] Run /sbin/init as init process

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
---
 drivers/nvme/host/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index a4d8c90ee7cc..04174a40b9b0 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -2074,7 +2074,7 @@ static int nvme_wait_ready(struct nvme_ctrl *ctrl, u64 cap, bool enabled)
 		if ((csts & NVME_CSTS_RDY) == bit)
 			break;
 
-		msleep(100);
+		usleep_range(1000, 2000);
 		if (fatal_signal_pending(current))
 			return -EINTR;
 		if (time_after(jiffies, timeout)) {
-- 
2.25.1