Blame SOURCES/kvm-cow-make-writes-go-at-a-less-indecent-speed.patch

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From a1a7f1301c20582d3326e33acd94a4c198c60bcd Mon Sep 17 00:00:00 2001
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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Fri, 18 Oct 2013 08:14:27 +0200
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Subject: [PATCH 02/81] cow: make writes go at a less indecent speed
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RH-Author: Paolo Bonzini <pbonzini@redhat.com>
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Message-id: <1382084091-16636-3-git-send-email-pbonzini@redhat.com>
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Patchwork-id: 54985
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O-Subject: [RHEL 7.0 qemu-kvm PATCH 02/26] cow: make writes go at a less indecent speed
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Bugzilla: 989646
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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Only sync once per write, rather than once per sector.
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Reviewed-by: Eric Blake <eblake@redhat.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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(cherry picked from commit 26ae980492920e417bc91761cc85950f18e41f85)
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---
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 block/cow.c | 19 ++++++++++++++++---
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 1 file changed, 16 insertions(+), 3 deletions(-)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 block/cow.c |   19 ++++++++++++++++---
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 1 files changed, 16 insertions(+), 3 deletions(-)
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diff --git a/block/cow.c b/block/cow.c
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index c12088b..2f72334 100644
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--- a/block/cow.c
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+++ b/block/cow.c
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@@ -106,7 +106,7 @@ static int cow_open(BlockDriverState *bs, QDict *options, int flags)
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  * XXX(hch): right now these functions are extremely inefficient.
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  * We should just read the whole bitmap we'll need in one go instead.
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  */
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-static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum)
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+static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum, bool *first)
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 {
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     uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
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     uint8_t bitmap;
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@@ -117,9 +117,21 @@ static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum)
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        return ret;
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     }
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+    if (bitmap & (1 << (bitnum % 8))) {
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+        return 0;
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+    }
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+
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+    if (*first) {
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+        ret = bdrv_flush(bs->file);
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+        if (ret < 0) {
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+            return ret;
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+        }
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+        *first = false;
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+    }
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+
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     bitmap |= (1 << (bitnum % 8));
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-    ret = bdrv_pwrite_sync(bs->file, offset, &bitmap, sizeof(bitmap));
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+    ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap));
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     if (ret < 0) {
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        return ret;
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     }
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@@ -181,9 +193,10 @@ static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
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 {
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     int error = 0;
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     int i;
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+    bool first = true;
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     for (i = 0; i < nb_sectors; i++) {
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-        error = cow_set_bit(bs, sector_num + i);
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+        error = cow_set_bit(bs, sector_num + i, &first);
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         if (error) {
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             break;
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         }
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-- 
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1.7.1
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