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From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: Max Reitz <mreitz@redhat.com>,
	qemu-devel@nongnu.org, qemu-block@nongnu.org
Cc: kwolf@redhat.com, den@openvz.org
Subject: Re: [Qemu-devel] [PATCH 3/7] qcow2: split out reading normal clusters from qcow2_co_preadv
Date: Mon, 1 Oct 2018 18:14:35 +0300	[thread overview]
Message-ID: <9e53e78b-a0ef-9486-1036-3737ba8cad11@virtuozzo.com> (raw)
In-Reply-To: <6e19aaeb-8acc-beb9-5ece-9ae6101637a9@redhat.com>

27.09.2018 20:35, Max Reitz wrote:
> On 07.08.18 19:43, Vladimir Sementsov-Ogievskiy wrote:
>> Memory allocation may become less efficient for encrypted case. It's a
>> payment for further asynchronous scheme.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> ---
>>   block/qcow2.c | 114 ++++++++++++++++++++++++++++++++--------------------------
>>   1 file changed, 64 insertions(+), 50 deletions(-)
>>
>> diff --git a/block/qcow2.c b/block/qcow2.c
>> index 65e3ca00e2..5e7f2ee318 100644
>> --- a/block/qcow2.c
>> +++ b/block/qcow2.c
>> @@ -1808,6 +1808,67 @@ out:
>>       return ret;
>>   }
>>   
>> +static coroutine_fn int qcow2_co_preadv_normal(BlockDriverState *bs,
>> +                                               uint64_t file_cluster_offset,
>> +                                               uint64_t offset,
>> +                                               uint64_t bytes,
>> +                                               QEMUIOVector *qiov,
>> +                                               uint64_t qiov_offset)
>> +{
>> +    int ret;
>> +    BDRVQcow2State *s = bs->opaque;
>> +    void *crypt_buf = NULL;
>> +    QEMUIOVector hd_qiov;
>> +    int offset_in_cluster = offset_into_cluster(s, offset);
>> +
>> +    if ((file_cluster_offset & 511) != 0) {
>> +        return -EIO;
>> +    }
>> +
>> +    qemu_iovec_init(&hd_qiov, qiov->niov);
> So you're not just re-allocating the bounce buffer for every single
> call, but also this I/O vector.  Hm.
>
>> +    if (bs->encrypted) {
>> +        assert(s->crypto);
>> +        assert(bytes <= QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);
>> +
>> +        crypt_buf = qemu_try_blockalign(bs->file->bs, bytes);
> 1. Why did you remove the comment?
>
> 2. The check for whether crypt_buf was successfully allocated is missing.
>
> 3. Do you have any benchmarks for encrypted images?  Having to allocate
> the bounce buffer for potentially every single cluster sounds rather bad
> to me.

Hmm, no excuses. 1- Will fix, 2 - will fix, 3 - will fix or at least 
test the performance.

>
>> +        qemu_iovec_add(&hd_qiov, crypt_buf, bytes);
>> +    } else {
>> +        qemu_iovec_concat(&hd_qiov, qiov, qiov_offset, bytes);
> qcow2_co_preadv() continues to do this as well.  That's superfluous now.

hd_qiov is local here.. or what do you mean?

>
>> +    }
>> +
>> +    BLKDBG_EVENT(bs->file, BLKDBG_READ_AIO);
>> +    ret = bdrv_co_preadv(bs->file,
>> +                         file_cluster_offset + offset_in_cluster,
>> +                         bytes, &hd_qiov, 0);
>> +    if (ret < 0) {
>> +        goto out;
>> +    }
>> +
>> +    if (bs->encrypted) {
>> +        assert(s->crypto);
>> +        assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
>> +        assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
>> +        if (qcrypto_block_decrypt(s->crypto,
>> +                                  (s->crypt_physical_offset ?
>> +                                   file_cluster_offset + offset_in_cluster :
>> +                                   offset),
>> +                                  crypt_buf,
>> +                                  bytes,
>> +                                  NULL) < 0) {
> What's the reason against decrypting this in-place in qiov so we could
> save the bounce buffer?  We allow offsets in clusters, so why can't we
> just call this function once per involved I/O vector entry?

Isn't it unsafe to do decryption in guest buffers?

>
> Max
>
>> +            ret = -EIO;
>> +            goto out;
>> +        }
>> +        qemu_iovec_from_buf(qiov, qiov_offset, crypt_buf, bytes);
>> +    }
>> +
>> +out:
>> +    qemu_vfree(crypt_buf);
>> +    qemu_iovec_destroy(&hd_qiov);
>> +
>> +    return ret;
>> +}
>> +
>>   static coroutine_fn int qcow2_co_preadv(BlockDriverState *bs, uint64_t offset,
>>                                           uint64_t bytes, QEMUIOVector *qiov,
>>                                           int flags)
>> @@ -1819,7 +1880,6 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState *bs, uint64_t offset,
>>       uint64_t cluster_offset = 0;
>>       uint64_t bytes_done = 0;
>>       QEMUIOVector hd_qiov;
>> -    uint8_t *cluster_data = NULL;
>>   
>>       qemu_iovec_init(&hd_qiov, qiov->niov);
>>   
>> @@ -1882,57 +1942,12 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState *bs, uint64_t offset,
>>           case QCOW2_CLUSTER_NORMAL:
>>               qemu_co_mutex_unlock(&s->lock);
>>   
>> -            if ((cluster_offset & 511) != 0) {
>> -                ret = -EIO;
>> -                goto fail_nolock;
>> -            }
>> -
>> -            if (bs->encrypted) {
>> -                assert(s->crypto);
>> -
>> -                /*
>> -                 * For encrypted images, read everything into a temporary
>> -                 * contiguous buffer on which the AES functions can work.
>> -                 */
>> -                if (!cluster_data) {
>> -                    cluster_data =
>> -                        qemu_try_blockalign(bs->file->bs,
>> -                                            QCOW_MAX_CRYPT_CLUSTERS
>> -                                            * s->cluster_size);
>> -                    if (cluster_data == NULL) {
>> -                        ret = -ENOMEM;
>> -                        goto fail_nolock;
>> -                    }
>> -                }
>> -
>> -                assert(cur_bytes <= QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);
>> -                qemu_iovec_reset(&hd_qiov);
>> -                qemu_iovec_add(&hd_qiov, cluster_data, cur_bytes);
>> -            }
>> -
>> -            BLKDBG_EVENT(bs->file, BLKDBG_READ_AIO);
>> -            ret = bdrv_co_preadv(bs->file,
>> -                                 cluster_offset + offset_in_cluster,
>> -                                 cur_bytes, &hd_qiov, 0);
>> +            ret = qcow2_co_preadv_normal(bs, cluster_offset,
>> +                                         offset, cur_bytes, qiov, bytes_done);
>>               if (ret < 0) {
>>                   goto fail_nolock;
>>               }
>> -            if (bs->encrypted) {
>> -                assert(s->crypto);
>> -                assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
>> -                assert((cur_bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
>> -                if (qcrypto_block_decrypt(s->crypto,
>> -                                          (s->crypt_physical_offset ?
>> -                                           cluster_offset + offset_in_cluster :
>> -                                           offset),
>> -                                          cluster_data,
>> -                                          cur_bytes,
>> -                                          NULL) < 0) {
>> -                    ret = -EIO;
>> -                    goto fail_nolock;
>> -                }
>> -                qemu_iovec_from_buf(qiov, bytes_done, cluster_data, cur_bytes);
>> -            }
>> +
>>               qemu_co_mutex_lock(&s->lock);
>>               break;
>>   
>> @@ -1953,7 +1968,6 @@ fail:
>>   
>>   fail_nolock:
>>       qemu_iovec_destroy(&hd_qiov);
>> -    qemu_vfree(cluster_data);
>>   
>>       return ret;
>>   }
>>
>


-- 
Best regards,
Vladimir

  parent reply	other threads:[~2018-10-01 15:14 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-07 17:43 [Qemu-devel] [PATCH 0/7] qcow2: async handling of fragmented io Vladimir Sementsov-Ogievskiy
2018-08-07 17:43 ` [Qemu-devel] [PATCH 1/7] qcow2: move qemu_co_mutex_lock below decryption procedure Vladimir Sementsov-Ogievskiy
     [not found]   ` <8e1cc18c-307f-99b1-5892-713ebd17a15f@redhat.com>
     [not found]     ` <43277786-b6b9-e18c-b0ca-064ff7c9c0c9@redhat.com>
2018-10-01 15:56       ` Vladimir Sementsov-Ogievskiy
2018-08-07 17:43 ` [Qemu-devel] [PATCH 2/7] qcow2: bdrv_co_pwritev: move encryption code out of lock Vladimir Sementsov-Ogievskiy
2018-08-07 17:43 ` [Qemu-devel] [PATCH 3/7] qcow2: split out reading normal clusters from qcow2_co_preadv Vladimir Sementsov-Ogievskiy
     [not found]   ` <6e19aaeb-8acc-beb9-5ece-9ae6101637a9@redhat.com>
2018-10-01 15:14     ` Vladimir Sementsov-Ogievskiy [this message]
2018-10-01 15:39       ` Max Reitz
2018-10-01 16:00         ` Vladimir Sementsov-Ogievskiy
2018-11-01 12:17     ` Vladimir Sementsov-Ogievskiy
2018-11-07 13:51       ` Max Reitz
2018-11-07 18:16       ` Kevin Wolf
2018-11-08 10:02         ` Vladimir Sementsov-Ogievskiy
2018-11-08 10:33           ` Kevin Wolf
2018-11-08 12:36             ` Vladimir Sementsov-Ogievskiy
2018-08-07 17:43 ` [Qemu-devel] [PATCH 4/7] qcow2: async scheme for qcow2_co_preadv Vladimir Sementsov-Ogievskiy
     [not found]   ` <08a610aa-9c78-1c83-5e48-b93080aac87b@redhat.com>
2018-10-01 15:33     ` Vladimir Sementsov-Ogievskiy
2018-10-01 15:49       ` Max Reitz
2018-10-01 16:17         ` Vladimir Sementsov-Ogievskiy
2018-08-07 17:43 ` [Qemu-devel] [PATCH 5/7] qcow2: refactor qcow2_co_pwritev: split out qcow2_co_do_pwritev Vladimir Sementsov-Ogievskiy
     [not found]   ` <5c871ce7-2cab-f897-0b06-cbc05b9ffe97@redhat.com>
2018-10-01 15:43     ` Vladimir Sementsov-Ogievskiy
2018-10-01 15:50       ` Max Reitz
2018-08-07 17:43 ` [Qemu-devel] [PATCH 6/7] qcow2: refactor qcow2_co_pwritev locals scope Vladimir Sementsov-Ogievskiy
2018-08-07 17:43 ` [Qemu-devel] [PATCH 7/7] qcow2: async scheme for qcow2_co_pwritev Vladimir Sementsov-Ogievskiy
     [not found]   ` <1c8299bf-0b31-82a7-c7c4-5069581f2d94@redhat.com>
2018-10-01 15:46     ` Vladimir Sementsov-Ogievskiy
2018-08-16  0:51 ` [Qemu-devel] [PATCH 0/7] qcow2: async handling of fragmented io Max Reitz
2018-08-16 13:58   ` Vladimir Sementsov-Ogievskiy
2018-08-17 19:34     ` Max Reitz
2018-08-17 19:43       ` Denis V. Lunev
2018-08-20 16:33       ` Vladimir Sementsov-Ogievskiy
2018-08-20 16:39         ` Max Reitz

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