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Re: [Qemu-devel] [PATCH v3 1/5] block: split write_zeroes always
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH v3 1/5] block: split write_zeroes always |
Date: |
Thu, 26 May 2016 16:51:57 +0800 |
User-agent: |
Mutt/1.6.1 (2016-04-27) |
On Wed, 05/25 21:48, Eric Blake wrote:
> From: "Denis V. Lunev" <address@hidden>
>
> We should split requests even if they are less than write_zeroes_alignment.
> For example we can have the following request:
> offset 62k
> size 4k
> write_zeroes_alignment 64k
> The original code sent 1 request covering 2 qcow2 clusters, and resulted
> in both clusters being allocated. But by splitting the request, we can
> cater to the case where one of the two clusters can be zeroed as a
> whole, for only 1 cluster allocated after the operation.
>
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Eric Blake <address@hidden>
> CC: Kevin Wolf <address@hidden>
> Message-Id: <address@hidden>
>
> [eblake: Avoid exceeding nb_sectors, hoist alignment checks out of
> loop, and update testsuite to show that patch works]
>
> Signed-off-by: Eric Blake <address@hidden>
> ---
> block/io.c | 30 +++++++++++++++++-------------
> tests/qemu-iotests/154.out | 18 ++++++++++++------
> 2 files changed, 29 insertions(+), 19 deletions(-)
>
> diff --git a/block/io.c b/block/io.c
> index f474b9a..26b5845 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -1118,28 +1118,32 @@ static int coroutine_fn
> bdrv_co_do_write_zeroes(BlockDriverState *bs,
> struct iovec iov = {0};
> int ret = 0;
> bool need_flush = false;
> + int head = 0;
> + int tail = 0;
>
> int max_write_zeroes = MIN_NON_ZERO(bs->bl.max_write_zeroes,
> BDRV_REQUEST_MAX_SECTORS);
> + if (bs->bl.write_zeroes_alignment) {
> + assert(is_power_of_2(bs->bl.write_zeroes_alignment));
> + head = sector_num & (bs->bl.write_zeroes_alignment - 1);
> + tail = (sector_num + nb_sectors) & (bs->bl.write_zeroes_alignment -
> 1);
> + max_write_zeroes &= ~(bs->bl.write_zeroes_alignment - 1);
> + }
>
> while (nb_sectors > 0 && !ret) {
> int num = nb_sectors;
>
> /* Align request. Block drivers can expect the "bulk" of the request
> - * to be aligned.
> + * to be aligned, and that unaligned requests do not cross cluster
> + * boundaries.
> */
> - if (bs->bl.write_zeroes_alignment
> - && num > bs->bl.write_zeroes_alignment) {
> - if (sector_num % bs->bl.write_zeroes_alignment != 0) {
> - /* Make a small request up to the first aligned sector. */
> - num = bs->bl.write_zeroes_alignment;
> - num -= sector_num % bs->bl.write_zeroes_alignment;
> - } else if ((sector_num + num) % bs->bl.write_zeroes_alignment !=
> 0) {
> - /* Shorten the request to the last aligned sector. num
> cannot
> - * underflow because num > bs->bl.write_zeroes_alignment.
> - */
> - num -= (sector_num + num) % bs->bl.write_zeroes_alignment;
> - }
> + if (head) {
> + /* Make a small request up to the first aligned sector. */
> + num = MIN(nb_sectors, bs->bl.write_zeroes_alignment - head);
> + head = 0;
> + } else if (tail && num > bs->bl.write_zeroes_alignment) {
> + /* Shorten the request to the last aligned sector. */
> + num -= tail;
> }
>
> /* limit request size */
> diff --git a/tests/qemu-iotests/154.out b/tests/qemu-iotests/154.out
> index 8946b73..b9d27c5 100644
> --- a/tests/qemu-iotests/154.out
> +++ b/tests/qemu-iotests/154.out
> @@ -106,11 +106,14 @@ read 1024/1024 bytes at offset 67584
> read 5120/5120 bytes at offset 68608
> 5 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> [{ "start": 0, "length": 32768, "depth": 1, "zero": true, "data": false},
> -{ "start": 32768, "length": 8192, "depth": 0, "zero": false, "data": true,
> "offset": 20480},
> +{ "start": 32768, "length": 4096, "depth": 0, "zero": false, "data": true,
> "offset": 20480},
> +{ "start": 36864, "length": 4096, "depth": 0, "zero": true, "data": false},
> { "start": 40960, "length": 8192, "depth": 1, "zero": true, "data": false},
> -{ "start": 49152, "length": 8192, "depth": 0, "zero": false, "data": true,
> "offset": 28672},
> +{ "start": 49152, "length": 4096, "depth": 0, "zero": false, "data": true,
> "offset": 24576},
> +{ "start": 53248, "length": 4096, "depth": 0, "zero": true, "data": false},
> { "start": 57344, "length": 8192, "depth": 1, "zero": true, "data": false},
> -{ "start": 65536, "length": 8192, "depth": 0, "zero": false, "data": true,
> "offset": 36864},
> +{ "start": 65536, "length": 4096, "depth": 0, "zero": false, "data": true,
> "offset": 28672},
> +{ "start": 69632, "length": 4096, "depth": 0, "zero": true, "data": false},
> { "start": 73728, "length": 134144000, "depth": 1, "zero": true, "data":
> false}]
>
> == spanning two clusters, non-zero after request ==
> @@ -145,11 +148,14 @@ read 7168/7168 bytes at offset 65536
> read 1024/1024 bytes at offset 72704
> 1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> [{ "start": 0, "length": 32768, "depth": 1, "zero": true, "data": false},
> -{ "start": 32768, "length": 8192, "depth": 0, "zero": false, "data": true,
> "offset": 20480},
> +{ "start": 32768, "length": 4096, "depth": 0, "zero": true, "data": false},
> +{ "start": 36864, "length": 4096, "depth": 0, "zero": false, "data": true,
> "offset": 20480},
> { "start": 40960, "length": 8192, "depth": 1, "zero": true, "data": false},
> -{ "start": 49152, "length": 8192, "depth": 0, "zero": false, "data": true,
> "offset": 28672},
> +{ "start": 49152, "length": 4096, "depth": 0, "zero": true, "data": false},
> +{ "start": 53248, "length": 4096, "depth": 0, "zero": false, "data": true,
> "offset": 24576},
> { "start": 57344, "length": 8192, "depth": 1, "zero": true, "data": false},
> -{ "start": 65536, "length": 8192, "depth": 0, "zero": false, "data": true,
> "offset": 36864},
> +{ "start": 65536, "length": 4096, "depth": 0, "zero": true, "data": false},
> +{ "start": 69632, "length": 4096, "depth": 0, "zero": false, "data": true,
> "offset": 28672},
> { "start": 73728, "length": 134144000, "depth": 1, "zero": true, "data":
> false}]
>
> == spanning two clusters, partially overwriting backing file ==
> --
> 2.5.5
>
Reviewed-by: Fam Zheng <address@hidden>
- [Qemu-devel] [PATCH v3 0/5] qcow2_co_write_zeroes and related improvements, Eric Blake, 2016/05/25
- [Qemu-devel] [PATCH v3 2/5] qcow2: simplify logic in qcow2_co_write_zeroes, Eric Blake, 2016/05/25
- [Qemu-devel] [PATCH v3 1/5] block: split write_zeroes always, Eric Blake, 2016/05/25
- Re: [Qemu-devel] [PATCH v3 1/5] block: split write_zeroes always,
Fam Zheng <=
- [Qemu-devel] [PATCH v3 3/5] qcow2: add tracepoints for qcow2_co_write_zeroes, Eric Blake, 2016/05/25
- [Qemu-devel] [PATCH v3 4/5] qemu-iotests: Test one more spot for optimizing write_zeroes, Eric Blake, 2016/05/25
- [Qemu-devel] [PATCH v3 5/5] qcow2: Catch more unaligned write_zero into zero cluster, Eric Blake, 2016/05/25