On 3 May 2011 22:02, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Tuesday 03 May 2011 20:54:43 Per Forlin wrote: >> >> page_not_up_to_date: >> >> /* Get exclusive access to the page ... */ >> >> error = lock_page_killable(page); >> > I looked at the code in do_generic_file_read(). lock_page_killable >> > waits until the current read ahead is completed. >> > Is it possible to configure the read ahead to push multiple read >> > request to the block device queue?add > > I believe sleeping in __lock_page_killable is the best possible scenario. > Most cards I've seen work best when you use at least 64KB reads, so it will > be faster to wait there than to read smaller units. > >> When I first looked at this I used dd if=/dev/mmcblk0 of=/dev/null bs=1M count=4 >> If bs is larger than read ahead, this will make the execution loop in >> do_generic_file_read() reading 512 until 1M is read. The second time >> in this loop it will wait on lock_page_killable. >> >> If bs=16k the execution wont stuck at lock_page_killable. > > submitting small 512 byte read requests is a real problem when the > underlying page size is 16 KB. If your interpretation is right, > we should probably find a way to make it read larger chunks > on flash media. Sorry a typo. I missed out a "k" :) It reads 512k until 1M. > > Arnd > Per -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
