Am 30.01.2015 um 22:15 schrieb Kevin Wolf:
> Am 30.01.2015 um 22:05 hat Peter Lieven geschrieben:
>> Am 30.01.2015 um 18:16 schrieb Max Reitz:
>>> On 2015-01-30 at 09:33, Peter Lieven wrote:
>>>> this patch finally introduces multiread support to virtio-blk. While
>>>> multiwrite support was there for a long time, read support was missing.
>>>>
>>>> The complete merge logic is moved into virtio-blk.c which has
>>>> been the only user of request merging ever since. This is required
>>>> to be able to merge chunks of requests and immediately invoke callbacks
>>>> for those requests. Secondly, this is required to switch to
>>>> direct invocation of coroutines which is planned at a later stage.
>>>>
>>>> The following benchmarks show the performance of running fio with
>>>> 4 worker threads on a local ram disk. The numbers show the average
>>>> of 10 test runs after 1 run as warmup phase.
>>>>
>>>> | 4k | 64k | 4k
>>>> MB/s | rd seq | rd rand | rd seq | rd rand | wr seq | wr rand
>>>> --------------+--------+---------+--------+---------+--------+--------
>>>> master | 1221 | 1187 | 4178 | 4114 | 1745 | 1213
>>>> multiread | 1829 | 1189 | 4639 | 4110 | 1894 | 1216
>>>>
>>>> Signed-off-by: Peter Lieven <p...@kamp.de>
>>>> ---
>>>> hw/block/dataplane/virtio-blk.c | 8 +-
>>>> hw/block/virtio-blk.c | 288
>>>> +++++++++++++++++++++++++++-------------
>>>> include/hw/virtio/virtio-blk.h | 19 +--
>>>> trace-events | 1 +
>>>> 4 files changed, 210 insertions(+), 106 deletions(-)
>>>> + int64_t sector_num = 0;
>>>> +
>>>> + if (mrb->num_reqs == 1) {
>>>> + virtio_submit_multireq2(blk, mrb, 0, 1, -1);
>>>> + mrb->num_reqs = 0;
>>>> return;
>>>> }
>>>> - ret = blk_aio_multiwrite(blk, mrb->blkreq, mrb->num_writes);
>>>> - if (ret != 0) {
>>>> - for (i = 0; i < mrb->num_writes; i++) {
>>>> - if (mrb->blkreq[i].error) {
>>>> - virtio_blk_rw_complete(mrb->blkreq[i].opaque, -EIO);
>>>> + max_xfer_len = blk_get_max_transfer_length(mrb->reqs[0]->dev->blk);
>>>> + max_xfer_len = MIN_NON_ZERO(max_xfer_len, INT_MAX);
>>>> +
>>>> + qsort(mrb->reqs, mrb->num_reqs, sizeof(*mrb->reqs),
>>>> + &virtio_multireq_compare);
>>>> +
>>>> + for (i = 0; i < mrb->num_reqs; i++) {
>>>> + VirtIOBlockReq *req = mrb->reqs[i];
>>>> + if (num_reqs > 0) {
>>>> + bool merge = true;
>>>> +
>>>> + /* merge would exceed maximum number of IOVs */
>>>> + if (niov + req->qiov.niov + 1 > IOV_MAX) {
>>> Hm, why the +1?
>> A really good question. I copied this piece from the old merge routine. It
>> seems
>> definetely wrong.
> The old code merged requests even if they were overlapping. This could
> result in one area being split in two.
>
> I think you don't support this here, so removing the + 1 is probably
> okay.
I don't support it because it was a good source for bugs in the past and I think
a good guest should not create overlapping requests at all.
Peter
