On Thu, 20 May 2010, Miklos Szeredi wrote: > > With Jens' pipe growing patch and additional fuse patches it was > possible to achieve a 20GBytes/s write throghput on my laptop in a > "null" filesystem (no page cache, data goes to /dev/null). Btw, I don't think that is a very interesting benchmark. The reason I say that is that many man years ago I played with doing zero-copy pipe read/write system calls (no splice, just automatic "follow the page tables, mark things read-only etc" things). It was considered sexy to do things like that during the mid-90's - there were all the crazy ukernel people with Mach etc doing magic things with moving pages around. It got me a couple of gigabytes per second back then (when memcpy() speeds were in the tens of megabytes) on benchmarks like lmbench that just wrote the same buffer over and over again without ever touching the data. It was totally worthless on _any_ real load. In fact, it made things worse. I never found a single case where it helped. So please don't ever benchmark things that don't make sense, and then use the numbers as any kind of reason to do anything. It's worse than worthless. It actually adds negative value to show "look ma, no hands" for things that nobody does. It makes people think it's a good idea, and optimizes the wrong thing entirely. Are there actual real loads that get improved? I don't care if it means that the improvement goes from three orders of magnitude to just a couple of percent. The "couple of percent on actual loads" is a lot more important than "many orders of magnitude on a made-up benchmark". Linus -- 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
