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author | Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> | 2010-04-19 16:56:41 +0100 |
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committer | Kevin Wolf <kwolf@redhat.com> | 2010-05-03 10:07:32 +0200 |
commit | 51762288b41f59d027073c404a29256fc4d4540e (patch) | |
tree | bd81fbd9db389001c8715a1f5a1fb3bc54574c83 /qemu-img.c | |
parent | 4899d10d142e97eea8f64141a3507b2ee1a64f52 (diff) | |
download | qemu-51762288b41f59d027073c404a29256fc4d4540e.zip qemu-51762288b41f59d027073c404a29256fc4d4540e.tar.gz qemu-51762288b41f59d027073c404a29256fc4d4540e.tar.bz2 |
block: Cache total_sectors to reduce bdrv_getlength calls
The BlockDriver bdrv_getlength function is called from the I/O code path
when checking that the request falls within the device. Unfortunately
this involves an lseek system call in the raw protocol; every read or
write request will incur this lseek cost.
Jan Kiszka <jan.kiszka@siemens.com> identified this issue and its
latency overhead. This patch caches device length in the existing
total_sectors variable so lseek calls can be avoided for fixed size
devices.
Growable devices fall back to the full bdrv_getlength code path because
I have not added logic to detect extending the size of the device in a
write.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'qemu-img.c')
0 files changed, 0 insertions, 0 deletions