On Tue, May 19, 2015 at 10:58:43PM +0300, Adrian Hunter wrote: > On 19/05/2015 5:48 p.m., Namhyung Kim wrote: > >Hi Adrian, > > > >On Tue, May 19, 2015 at 04:05:46PM +0300, Adrian Hunter wrote: > >>Patch "perf tools: Protect dso cache fd with a mutex" > >>changed data_file_size() to open the data file if it > >>was not open. > >> > >>data_read_offset() was calling data_file_size() to read > >>the data file size, but data_file_size() can fail to > >>open the file because the binary_type has not been set up. > >> > >>The correct function to call is dso__data_size() which > >>uses dso__data_fd() to open the file correctly. > > > >Right, but I worried about the locking overhead. By using > >dso__data_size() it'll call dso__data_fd() everytime which grabs the > >dso__data_open_lock that is a global mutex. It can be a performance > >bottleneck on multi-thread report IMHO. > > > >I assumed that correct code should check the data fd or size before > >calling read function as I read the comment in dso.h file. > > > >What about adding the missing check in a proper place instead? > > It looks to me like you need to change data_file_size() and > dso_cache__read() so that they open the fd properly i.e. call > dso__data_fd() instead of open_dso().
OK, I'll change it to have a proper binary type before calling open_dso() like dso__data_fd() does. But I still think it's good to open data fd explicitly before reading from dso cache. > > dso__data_fd() should not be taking a lock because the lock must > be held while the fd in being used. > > Perhaps there should be dso__get_fd() and dso__put_fd() that lock/open > and the unlock. That is already a part of my patchset but not merged yet. > > But I will have to leave this to you because I am snowed with > my own problems. No problem. I can see you're doing hardwork ;-) Thanks, Namhyung -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
