Thanks for your thought! It may not make much sense. Because I think the probability of two bios have the same start sector and the situation mentioned by Ming Lei is too low. Thanks , Bonben
2013/10/25 Ming Lei <tom.leim...@gmail.com>: > On Wed, Oct 23, 2013 at 6:59 PM, Jan Kara <j...@suse.cz> wrote: >> On Wed 23-10-13 08:47:44, 韩磊 wrote: >>> Nowadays,the IO schedulers in linux kernel have four types: >>> >>> deadline,noop,Anticiptory and CFQ.CFQ is the default scheduler.But CFQ is >>> not a good scheduler for SSD,dealine may be a good choice. >> >>> When deadline runs,it has a mount of computation about merging and >>> sorting.Merge has three types: front_merge,no_merge and back_merge. >>> Why don't have another type: merge based same sector.For example,it have >>> two bios in a request list,theyboth have the same bi->sector,the bi->size >>> maybe not equal. Whether can we put the latter bio replace the former?What >>> do you find that significant?Or the other levels in OS has finished this >>> function? >> That doesn't make much sense to me. If there are two bios in flight for >> some sector, results are undefined. Thus we usually avoid such situation >> (usually we want to have defined contents of the disk :). The exclusion is >> usually achieved at higher level using page locking etc. So adding code >> speeding up such requests doesn't seem worth it. > > The situation might be triggered when same file is read from two tasks, > one is read via page cache, and another one is read by O_DIRECT. > > But still not sure if that makes sense. > > Thanks, > -- > Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
