On Tue, Jul 10, 2012 at 07:57:55PM -0600, Liu Bo wrote: > On 07/11/2012 02:58 AM, Josef Bacik wrote: > > > On Tue, Jul 10, 2012 at 05:27:59AM -0600, Liu Bo wrote: > >> While testing with my buffer read fio jobs[1], I find that btrfs does not > >> perform well enough. > >> > >> Here is a scenario in fio jobs: > >> > >> We have 4 threads, "t1 t2 t3 t4", starting to buffer read a same file, > >> and all of them will race on add_to_page_cache_lru(), and if one thread > >> successfully puts its page into the page cache, it takes the responsibility > >> to read the page's data. > >> > >> And what's more, reading a page needs a period of time to finish, in which > >> other threads can slide in and process rest pages: > >> > >> t1 t2 t3 t4 > >> add Page1 > >> read Page1 add Page2 > >> | read Page2 add Page3 > >> | | read Page3 add Page4 > >> | | | read Page4 > >> -----|------------|-----------|-----------|-------- > >> v v v v > >> bio bio bio bio > >> > >> Now we have four bios, each of which holds only one page since we need to > >> maintain consecutive pages in bio. Thus, we can end up with far more bios > >> than we need. > >> > >> Here we're going to > >> a) delay the real read-page section and > >> b) try to put more pages into page cache. > >> > >> With that said, we can make each bio hold more pages and reduce the number > >> of bios we need. > >> > >> Here is some numbers taken from fio results: > >> w/o patch w patch > >> ------------- -------- --------------- > >> READ: 745MB/s +32% 987MB/s > >> > > > > Um, I have this in btrfs-next > > > > Btrfs: use large extent range for read and its endio > > > > that seems to do the same thing, did you not want to do that anymore? Thanks, > > > > > > I'm still hard working on that patchset. :) > > Although the patchset is well worthy of testing, it is not good enough for btrfs upstream. > > While doing some tuning work on it, I realized that I could make this improvement without > the help of rwlock extent state stuff, so I made this smaller and cleaner patch for upstream > so that we could gain some performance here first. > So do you want me to drop the rwlock stuff and take this instead? Take a look at whats in btrfs-next and tell me what I should drop. Thanks, Josef -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
