On 07/14/2015 06:37 AM, Oleg Nesterov wrote: > On 07/14, Jan Kara wrote: >> So unless >> I'm missing something and there is a significant performance advantage to >> Dave's patches I'm all for using a generic primitive you suggest. > > I think percpu_rw_semaphore looks a bit better. And even a bit faster. > And it will not block __sb_start_write() entirely while freeze_super() > sleeps in synchronize_rcu().
That's true, but freeze_super() and the code blocked by it is a super-rare path compared with write(). > freeze_super() should be faster too after rcu_sync changes, but this > is not that important. > > But again, to me the main advantage is that we can use the generic > primitives and remove this nontrivial code in fs/super.c. > >> Can you perhaps work with Dave on some common resolution? > > Dave, what do you think? Will you agree with percpu_rw_semaphore ? Using my little write-1-byte test (under will-it-scale), your 4 patches improves the number of writes/sec by 12%. My 3 patches improve the number of writes/sec by 32%. My patches manage to get rid of the memory barriers entirely in the fast path. Your approach keeps the barriers. Test: https://www.sr71.net/~dave/intel/write1byte.c -- 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/
