linux-kernel - [RFC v2 19/21] nvme-pci: precalculate number of DMA entries for each command

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Message-ID: <8c5b0e5ab1716166fc93e76cb2d3e01ca9cf8769.1726138681.git.leon@kernel.org>
Date: Thu, 12 Sep 2024 14:15:54 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Jens Axboe <axboe@...nel.dk>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Robin Murphy <robin.murphy@....com>,
	Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Keith Busch <kbusch@...nel.org>,
	Christoph Hellwig <hch@....de>,
	"Zeng, Oak" <oak.zeng@...el.com>,
	Chaitanya Kulkarni <kch@...dia.com>
Cc: Leon Romanovsky <leonro@...dia.com>,
	Sagi Grimberg <sagi@...mberg.me>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Jérôme Glisse <jglisse@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-rdma@...r.kernel.org,
	iommu@...ts.linux.dev,
	linux-nvme@...ts.infradead.org,
	linux-pci@...r.kernel.org,
	kvm@...r.kernel.org,
	linux-mm@...ck.org
Subject: [RFC v2 19/21] nvme-pci: precalculate number of DMA entries for each command

From: Leon Romanovsky <leonro@...dia.com>

Calculate the number of DMA entries for each command in the request in
advance.

Signed-off-by: Leon Romanovsky <leonro@...dia.com>
---
 drivers/nvme/host/pci.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index a9a66f184138..2b236b1d209e 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -231,6 +231,7 @@ struct nvme_iod {
 	struct nvme_request req;
 	struct nvme_command cmd;
 	bool aborted;
+	u8 nr_dmas;
 	s8 nr_allocations;	/* PRP list pool allocations. 0 means small
 				   pool in use */
 	dma_addr_t first_dma;
@@ -766,6 +767,23 @@ static blk_status_t nvme_map_metadata(struct nvme_dev *dev, struct request *req,
 	return BLK_STS_OK;
 }
 
+static u8 nvme_calc_num_dmas(struct request *req)
+{
+	struct bio_vec bv;
+	u8 nr_dmas;
+
+	if (blk_rq_nr_phys_segments(req) == 0)
+		return 0;
+
+	nr_dmas = DIV_ROUND_UP(blk_rq_payload_bytes(req), NVME_CTRL_PAGE_SIZE);
+	bv = req_bvec(req);
+	if (bv.bv_offset && (bv.bv_offset + bv.bv_len) >= NVME_CTRL_PAGE_SIZE)
+		/* Accommodate for unaligned first page */
+		nr_dmas++;
+
+	return nr_dmas;
+}
+
 static blk_status_t nvme_prep_rq(struct nvme_dev *dev, struct request *req)
 {
 	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
@@ -779,6 +797,8 @@ static blk_status_t nvme_prep_rq(struct nvme_dev *dev, struct request *req)
 	if (ret)
 		return ret;
 
+	iod->nr_dmas = nvme_calc_num_dmas(req);
+
 	if (blk_rq_nr_phys_segments(req)) {
 		ret = nvme_map_data(dev, req, &iod->cmd);
 		if (ret)
-- 
2.46.0