[PATCH] nvme: add NO_FUA quirk for ADATA XPG GAMMIX S70 BLADE

[Hugo Deco]

On the ADATA XPG GAMMIX S70 BLADE (PCI 1cc1:5370, firmware 03020P5E)
every Write with the FUA bit set takes 200, 400 or 600 ms to complete,
always a multiple of ~200 ms, while a plain Write completes in
0.0-0.4 ms and a Flush in ~1.3 ms. Tracing nvme_setup_cmd and
nvme_complete_rq shows the whole delay is between submission and
completion, i.e. inside the device (e.g. FUA write, control 0x4000:
598.3 ms).

Because ext4/jbd2 issue FUA for every journal commit, fsync() on this
drive stalls for 250-890 ms and desktop applications freeze.

Add NVME_QUIRK_NO_FUA, which stops advertising BLK_FEAT_FUA while
keeping the volatile write cache enabled, so the block layer emulates
FUA with a Write followed by a Flush. Durability semantics are
unchanged.

With the quirk applied, 4 KiB O_DIRECT|O_DSYNC writes and
create+write+fsync drop from 250-890 ms to a 0.82-0.85 ms median
(30 samples, two partitions on the same drive).

Signed-off-by: Hugo Deco <hugodeco at sufficit.com.br>
---
 drivers/nvme/host/core.c | 11 +++++++++++
 drivers/nvme/host/nvme.h |  8 ++++++++
 2 files changed, 19 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 7eb0f9f..5c0d74d 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -2477,6 +2477,8 @@ static int nvme_update_ns_info_block(struct nvme_ns *ns,
 		lim.features |= BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA;
 	else
 		lim.features &= ~(BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA);
+	if (ns->ctrl->quirks & NVME_QUIRK_NO_FUA)
+		lim.features &= ~BLK_FEAT_FUA;

 	if (info->is_rotational)
 		lim.features |= BLK_FEAT_ROTATIONAL;
@@ -3090,6 +3092,15 @@ struct nvme_core_quirk_entry {
 };

 static const struct nvme_core_quirk_entry core_quirks[] = {
+	{
+		/*
+		 * ADATA XPG GAMMIX S70 BLADE (fw 03020P5E) takes 200-600 ms
+		 * to complete FUA writes while Flush takes ~1.3 ms.
+		 */
+		.vid = 0x1cc1,
+		.mn = "XPG GAMMIX S70 BLADE",
+		.quirks = NVME_QUIRK_NO_FUA,
+	},
 	{
 		/*
 		 * This Toshiba device seems to die using any APST states.  See:
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index a643c47..2128b40 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -183,6 +183,12 @@ enum nvme_quirks {
 	 * Admin queue DMA buffers must be page aligned
 	 */
 	NVME_QUIRK_ADMIN_PAGE_ALIGN		= (1 << 23),
+
+	/*
+	 * The device is extremely slow on FUA writes but fast on Flush;
+	 * do not advertise FUA so the block layer emulates it.
+	 */
+	NVME_QUIRK_NO_FUA			= (1 << 24),
 };

 static inline char *nvme_quirk_name(enum nvme_quirks q)
@@ -236,6 +242,8 @@ static inline char *nvme_quirk_name(enum nvme_quirks q)
 		return "dmapool_align_512";
 	case NVME_QUIRK_ADMIN_PAGE_ALIGN:
 		return "admin_page_align";
+	case NVME_QUIRK_NO_FUA:
+		return "no_fua";
 	}

 	return "unknown";
-- 
2.53.0