Because if there are 4 cores doing heavy CPU lifting of 4 threads, when one is finished, you then waste time loading up the next thread because it's reading from the disk. If you have it already done with I/O it will be ready and less time is wasted.
Calvin On Apr 1, 2012 9:09 AM, "Baho Utot" <baho-u...@columbus.rr.com> wrote: > On 04/01/2012 08:37 AM, Calvin Morrison wrote: > >> Often higher cores benefit high I/O applications. If gcc is bottlenecking >> at reading and writing, sometimes more threads will help. >> > > How does that help? > > Sounds backwards to me > > > On Apr 1, 2012 7:49 AM, "Vitor > Garcia"<vitorlopesgarcia@**gmail.com<vitorlopesgar...@gmail.com>> >> wrote: >> >> On Sun, 01 Apr 2012 13:37:27 +0200 >>> Florian Pritz<bluew...@xinu.at> wrote: >>> >>> Simple tests (building readline because it's small) with -j4 and -j8 >>>> on my i7-920 show that -j8 is around 20% faster than -j4. IIRC >>>> wikipedia states that HT core can increase performance by up to 30%. >>>> >>> This is nice to know. I work with mechanichal engineering simulations >>> and we have noted that using more threads then avaiable processors (we >>> have a 2 x 6 cores processors that has HT, so it looks like a 24 cores >>> server) increases the calculation time on the softwares we have. I >>> assumed that the same would apply to any intensive task, and we have >>> even disabled HT on the BIOS. Perhaps I'll enable it again. >>> >>> >
