> -----Original Message----- > From: Jens Axboe [mailto:axboe@xxxxxxxxx] > Sent: Friday, December 21, 2012 7:33 AM > To: Sam Bradshaw (sbradshaw) > Cc: fio@xxxxxxxxxxxxxxx > Subject: Re: [PATCH] gettime: minimize integer division > > On 2012-12-20 20:23, Sam Bradshaw wrote: > > > > > > Something like this might work, though that amount of logic may > > be equivalent in terms of cycles to the divide. > > So I took a look at it. The costly bit is the division by > cycles_per_usec, which the compiler has no other option than turn into a > divq. The modulo and divide by 1M can be turned into something more > clever, basically shifts and imull. > > So how about the below? It turns the divq into multiplication and > division by 10M, which should be considerably less expensive. Can you > test and see how that works for you? That works much better. Several % lower execution time in fio_gettime(). IOPs look the same in my synthetic test but I'm not sure that's relevant; (it probably just needs some more tweaking). I'll keep hunting for other hot spots. -Sam ��.n��������+%������w��{.n�������^n�r������&��z�ޗ�zf���h���~����������_��+v���)ߣ�
