| Message ID | 1333097427-20912-1-git-send-email-zwu.kernel@gmail.com |
|---|---|
| State | New |
| Headers | show |
On Fri, Mar 30, 2012 at 9:50 AM, <zwu.kernel@gmail.com> wrote: > + * When all sync I/O drivers are converted to async I/O, it will be restored > + * to the original state. The problem here is that guess_disk_lchs() uses bdrv_read(), not whether device emulation uses sync or async I/O. Converting devices to async I/O will not fix this. Stefan
On Fri, Mar 30, 2012 at 6:29 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote: > On Fri, Mar 30, 2012 at 9:50 AM, <zwu.kernel@gmail.com> wrote: >> + * When all sync I/O drivers are converted to async I/O, it will be restored >> + * to the original state. > > The problem here is that guess_disk_lchs() uses bdrv_read(), not > whether device emulation uses sync or async I/O. Converting devices > to async I/O will not fix this. Yeah, but when all sync emulated devices drivers are converted to async mode, the code change need to be rolled back. This is what i mean. > > Stefan
On Fri, Mar 30, 2012 at 6:29 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote: > On Fri, Mar 30, 2012 at 9:50 AM, <zwu.kernel@gmail.com> wrote: >> + * When all sync I/O drivers are converted to async I/O, it will be restored >> + * to the original state. > > The problem here is that guess_disk_lchs() uses bdrv_read(), not > whether device emulation uses sync or async I/O. Converting devices > to async I/O will not fix this. By the way, when you did testing, you applied #1 of this patchset? I think that it make sense for that assert issue to be fixed. > > Stefan
On Sat, Mar 31, 2012 at 08:07:25PM +0800, Zhi Yong Wu wrote: > On Fri, Mar 30, 2012 at 6:29 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote: > > On Fri, Mar 30, 2012 at 9:50 AM, <zwu.kernel@gmail.com> wrote: > >> + * When all sync I/O drivers are converted to async I/O, it will be restored > >> + * to the original state. > > > > The problem here is that guess_disk_lchs() uses bdrv_read(), not > > whether device emulation uses sync or async I/O. Converting devices > > to async I/O will not fix this. > Yeah, but when all sync emulated devices drivers are converted to > async mode, the code change need to be rolled back. This is what i > mean. There are places outside device emulation that call bdrv_read(), like guest_disk_lchs() and bdrv_commit(). We would need to convert them before it's safe to remove the code to disable I/O throttling in bdrv_read()/bdrv_write(). It's not okay to drop the code before all bdrv_read()/bdrv_write() callers that are in a code path where I/O limits can be enabled have been fixed (including guest_disk_lchs()) because a request that exceeds I/O limits would cause QEMU to hang. Once all devices have been converted it might be possible to temporarily disable throttling in bdrv_read()/bdrv_write() and never disable it permanently. This is because the bdrv_read()/bdrv_write() calls would only come from QEMU code that is not directly driven by the guest - here we probably don't need to apply I/O limits anyway. In other words, devices use bdrv_aio_*() and I/O limits apply, QEMU internal code might still use bdrv_read()/bdrv_write() and limits will not apply. Anyway, I think it's best to drop this part of the comment because it's more related to the disable code in bdrv_read()/bdrv_write() than to this patch. Stefan
On Sat, Mar 31, 2012 at 08:09:46PM +0800, Zhi Yong Wu wrote: > On Fri, Mar 30, 2012 at 6:29 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote: > > On Fri, Mar 30, 2012 at 9:50 AM, <zwu.kernel@gmail.com> wrote: > >> + * When all sync I/O drivers are converted to async I/O, it will be restored > >> + * to the original state. > > > > The problem here is that guess_disk_lchs() uses bdrv_read(), not > > whether device emulation uses sync or async I/O. Converting devices > > to async I/O will not fix this. > By the way, when you did testing, you applied #1 of this patchset? I > think that it make sense for that assert issue to be fixed. Yes, I applied both patches 1 and 2. Stefan
diff --git a/block.c b/block.c index 1fbf4dd..6de6f89 100644 --- a/block.c +++ b/block.c @@ -1477,6 +1477,17 @@ static int bdrv_rw_co(BlockDriverState *bs, int64_t sector_num, uint8_t *buf, qemu_iovec_init_external(&qiov, &iov, 1); + /** + * In sync call context, when the vcpu is blocked, this throttling timer + * will not fire; so the I/O throttling function has to be disabled here + * if it has been enabled. + */ + if (bs->io_limits_enabled) { + fprintf(stderr, "Disabling I/O throttling on '%s' due " + "to synchronous I/O.\n", bdrv_get_device_name(bs)); + bdrv_io_limits_disable(bs); + } + if (qemu_in_coroutine()) { /* Fast-path if already in coroutine context */ bdrv_rw_co_entry(&rwco); @@ -1983,10 +1994,21 @@ static int guess_disk_lchs(BlockDriverState *bs, struct partition *p; uint32_t nr_sects; uint64_t nb_sectors; + bool enabled; bdrv_get_geometry(bs, &nb_sectors); + /** + * The function will be invoked during startup not only in sync I/O mode, + * but also in async I/O mode. So the I/O throttling function has to + * be disabled temporarily here, not permanently. + * When all sync I/O drivers are converted to async I/O, it will be restored + * to the original state. + */ + enabled = bs->io_limits_enabled; + bs->io_limits_enabled = false; ret = bdrv_read(bs, 0, buf, 1); + bs->io_limits_enabled = enabled; if (ret < 0) return -1; /* test msdos magic */