On 2/4/2014 12:55 PM, Phillip Susi wrote: > On 2/4/2014 1:43 PM, Stan Hoeppner wrote: >> Everything we've been discussing has been about maximizing write >> throughput. The fact that you argue this at this point makes it >> crystal clear that you don't have no understanding of the >> differences in the read/write paths and how buffer cache affects >> each differently. Further discussion is thus pointless. > > I am intimately familiar with the two code paths, having written > several applications using them, studied the kernel code extensively, > and been one of the original strong advocates for the kernel to grow > direct aio apis in the first place, since it worked swimmingly well on > WinNT. > > So I say again: switching to direct aio, while saving a decent chunk > of cpu time, makes very little difference in streaming write > throughput. If it did, there would be something terribly broken with > the buffer cache if it couldn't keep the disk queues full. If all this is true, then why do you keep making a tangential arguments that are not relevant? I never argued that the buffer cache path is slower. It is in fact much faster in most cases. I argued that accurately measuring the actual data throughput at the disks isn't possible when writing through buffer cache. At least not in a straightforward manner as with O_DIRECT. I've made the point in the last two or three replies. Yet instead of directly addressing that, rebutting that, you keep making these tangential irrelevant arguments... -- Stan -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
