On Tue, Jul 24, 2012 at 05:11:05PM +0530, Ankit Jain wrote: > > Currently, io_submit tries to execute the io requests on the > same thread, which could block because of various reaons (eg. > allocation of disk blocks). So, essentially, io_submit ends > up being a blocking call. Yup, sadly that's how its built. A blocking submission phase that returns once completion doesn't need the submitters's context. It happens to mostly work for O_DIRECT block IO most of the time. > With this patch, io_submit prepares all the kiocbs and then > adds (kicks) them to ctx->run_list (kicked) in one go and then > schedules the workqueue. The actual operations are not executed > on io_submit's process context, so it can return very quickly. Strong nack; this isn't safe without having done the work to ensure that all the task_struct references under the f_op->aio_*() paths won't be horribly confused to find a kernel thread instead of the process that called io_submit(). The one-off handling of the submitters's cred is an indication that there might be other cases to worry about :). > 3. Also, I tried not using aio_queue_work from io_submit call, and instead > depending on an already scheduled one or the iocbs being run when > io_getevents gets called. This seemed to give improved perfomance. But > does this constitute as change of api semantics? You can't rely on io_getevents() being called for forward progress. Its perfectly reasonable for a task to wait for io completion by polling an eventfd that aio_complete() notifies, for instance. - z -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
