Vivek Goyal <vgoyal@xxxxxxxxxx> writes: > On Fri, Jul 02, 2010 at 03:58:13PM -0400, Jeff Moyer wrote: > > [..] >> Changes from the last posting: >> - Yielding no longer expires the current queue. Instead, it sets up new >> requests from the target process so that they are issued in the yielding >> process' cfqq. This means that we don't need to worry about losing group >> or workload share. >> - Journal commits are now synchronous I/Os, which was required to get any >> sort of performance out of the fs_mark process in the presence of a >> competing reader. >> - WRITE_SYNC I/O no longer sets RQ_NOIDLE, for a similar reason. > > Hi Jeff, > > So this patchset relies on idling on WRITE_SYNC queues. Though in general > we don't have examples that why one should idle on processes doing WRITE_SYNC > IO because previous IO does not tell anything about the upcoming IO. I am > bringing up this point again to make sure that fundamentally we agree that > continue to idle on WRITE_SYNC is the right thing to do otherwise this patch > will fall apart. I think a mail server would be an example of an application that might do this. I'll see if I can get a real world test case (or perhaps some real world data) and verify that. I agree that if we choose not to idle on write's, then this approach can be thrown out the window. > I have yet to go through the patch in detail but allowing other queue to > dispatch requests in the same queue sounds like queue merging. So can > we use that semantics to say elv_merge_context() or elv_merge_queue() > instead of elv_yield(). In the code we can just merge the two queues when > the next request comes in and separate them out at the slice expiry I > guess. I considered that approach, but then you run into all of the questions about losing fairness across workloads and across groups. I believe the approach I've taken here is *significantly* simpler than merging and unmerging would be. Cheers, Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
