73 lines
2.9 KiB
Diff
73 lines
2.9 KiB
Diff
From 794d838efddc7e96f6e40c1c4bb2b1baf3c95cfb Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= <berrange@redhat.com>
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Date: Tue, 10 Jun 2025 13:37:01 +0100
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Subject: [PATCH 24/31] hw/nvme/ctrl: skip automatic zero-init of large arrays
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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RH-Author: Stefan Hajnoczi <stefanha@redhat.com>
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RH-MergeRequest: 461: Solve -ftrivial-auto-var-init performance regression with QEMU_UNINITIALIZED
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RH-Jira: RHEL-99887
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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RH-Commit: [23/30] 97877d2e280daf654f5893461c0bc9e6f6caa77d
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The 'nvme_map_sgl' method has a 256 element array used for copying
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data from the device. Skip the automatic zero-init of this array
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to eliminate the performance overhead in the I/O hot path.
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The 'segment' array will be fully initialized when reading data from
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the device.
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The 'nme_changed_nslist' method has a 4k byte array that is manually
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initialized with memset(). The compiler ought to be intelligent
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enough to turn the memset() into a static initialization operation,
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and thus not duplicate the automatic zero-init. Replacing memset()
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with '{}' makes it unambiguous that the array is statically initialized.
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Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
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Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
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Message-id: 20250610123709.835102-24-berrange@redhat.com
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit 7eeb1d3acc175813ad3d5e824f26123e0992093a)
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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---
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hw/nvme/ctrl.c | 6 +++---
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1 file changed, 3 insertions(+), 3 deletions(-)
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diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
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index 9f277b81d8..f000e2246f 100644
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--- a/hw/nvme/ctrl.c
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+++ b/hw/nvme/ctrl.c
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@@ -1047,7 +1047,8 @@ static uint16_t nvme_map_sgl(NvmeCtrl *n, NvmeSg *sg, NvmeSglDescriptor sgl,
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*/
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#define SEG_CHUNK_SIZE 256
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- NvmeSglDescriptor segment[SEG_CHUNK_SIZE], *sgld, *last_sgld;
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+ QEMU_UNINITIALIZED NvmeSglDescriptor segment[SEG_CHUNK_SIZE];
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+ NvmeSglDescriptor *sgld, *last_sgld;
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uint64_t nsgld;
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uint32_t seg_len;
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uint16_t status;
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@@ -5029,7 +5030,7 @@ static uint16_t nvme_error_info(NvmeCtrl *n, uint8_t rae, uint32_t buf_len,
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static uint16_t nvme_changed_nslist(NvmeCtrl *n, uint8_t rae, uint32_t buf_len,
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uint64_t off, NvmeRequest *req)
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{
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- uint32_t nslist[1024];
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+ uint32_t nslist[1024] = {};
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uint32_t trans_len;
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int i = 0;
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uint32_t nsid;
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@@ -5039,7 +5040,6 @@ static uint16_t nvme_changed_nslist(NvmeCtrl *n, uint8_t rae, uint32_t buf_len,
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return NVME_INVALID_FIELD | NVME_DNR;
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}
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- memset(nslist, 0x0, sizeof(nslist));
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trans_len = MIN(sizeof(nslist) - off, buf_len);
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while ((nsid = find_first_bit(n->changed_nsids, NVME_CHANGED_NSID_SIZE)) !=
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--
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2.39.3
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