Il 31/07/2014 11:47, Ming Lei ha scritto: >> Block mirroring of a device for example is done using coroutines. >> As block mirroring can be done on a raw device you need coroutines. > > If block layer knows the mirroring is in-progress, it still can enable > coroutine by ignoring bypass coroutine, or just let device disable > bypass coroutine in case of mirroring, and the current APIs are very > flexible.
What matters is not whether you're mirroring. What matters is whether you're calling bdrv_aio_readv/writev or bdrv_co_readv/writev. Under some limitation, if you are calling bdrv_aio_readv/writev you can bypass coroutines. (In fact drive mirroring uses those APIs too so it doesn't need coroutines and can benefit from the speedup too. :) But drive-backup does need them). The limitations are essentially "would bdrv_co_do_preadv or bdrv_co_do_pwritev do anything special?" This means for example for bdrv_co_do_pwritev: - bs->drv must be non-NULL - bs->read_only must be false - bdrv_check_byte_request(bs, offset, bytes) must return false - bs->io_limits_enabled must be false - the request must be aligned - (in bdrv_aligned_pwritev) the before_write_notifiers must be empty - (in bdrv_aligned_pwritev) bs->detect_zeroes must be off - (in bdrv_aligned_pwritev) the BDRV_REQ_ZERO_WRITE flag must be off - (in bdrv_aligned_pwritev) bs->enable_write_cache must be false and the hard part is organizing the code so that the code duplication is as limited as possible. Paolo
