Commit 586d1d65 authored by John Levon's avatar John Levon Committed by Jim Harris
Browse files

nvmf/vfio-user: don't read from completion entry 



We were accidentally reading the spdk_nvme_status from the CPL; on one
test, this was contributing to 2% of cache misses.

Signed-off-by: default avatarJohn Levon <john.levon@nutanix.com>
Change-Id: I7c967690458a183799f8d835360800d3094c3131
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/11849


Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Community-CI: Mellanox Build Bot
Tested-by: default avatarSPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: default avatarThanos Makatos <thanos.makatos@nutanix.com>
Reviewed-by: default avatarChangpeng Liu <changpeng.liu@intel.com>
Reviewed-by: default avatarJim Harris <james.r.harris@intel.com>
parent 7a9d089b

lib/nvmf/vfio_user.c

+13 −6
Original line number Diff line number Diff line
@@ -1086,8 +1086,9 @@ static int 
post_completion(struct nvmf_vfio_user_ctrlr *ctrlr, struct nvmf_vfio_user_cq *cq,

		uint32_t cdw0, uint16_t sqid, uint16_t cid, uint16_t sc, uint16_t sct)

{

	struct spdk_nvme_cpl *cpl;

	struct spdk_nvme_status cpl_status = { 0 };

	const struct spdk_nvmf_registers *regs;

	struct spdk_nvme_cpl *cpl;

	int err;



	assert(ctrlr != NULL);
@@ -1123,11 +1124,17 @@ post_completion(struct nvmf_vfio_user_ctrlr *ctrlr, struct nvmf_vfio_user_cq *cq 
	cpl->sqid = sqid;

	cpl->cid = cid;

	cpl->cdw0 = cdw0;

	cpl->status.dnr = 0x0;

	cpl->status.m = 0x0;

	cpl->status.sct = sct;

	cpl->status.sc = sc;

	cpl->status.p = cq->phase;



	/*

	 * This is a bitfield: instead of setting the individual bits we need

	 * directly in cpl->status, which would cause a read-modify-write cycle,

	 * we'll avoid reading from the CPL altogether by filling in a local

	 * cpl_status variable, then writing the whole thing.

	 */

	cpl_status.sct = sct;

	cpl_status.sc = sc;

	cpl_status.p = cq->phase;

	cpl->status = cpl_status;



	/* Ensure the Completion Queue Entry is visible. */

	spdk_wmb();