From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 12 Aug 1999 00:33:18 -0700 From: Richard Henderson To: Paul.Mackerras@cs.anu.edu.au Cc: Jes.Sorensen@cern.ch, Geert.Uytterhoeven@cs.kuleuven.ac.be, linuxppc-dev@lists.linuxppc.org, linux-fbdev@vuser.vu.union.edu, Richard Henderson Subject: Re: [linux-fbdev] Re: readl() and friends and eieio on PPC Message-ID: <19990812003318.A14941@cygnus.com> References: <199908100100.LAA28784@tango.anu.edu.au> <199908110023.KAA23996@tango.anu.edu.au> <19990811003805.A11890@cygnus.com> <199908120017.KAA25043@tango.anu.edu.au> <19990811214049.A14692@cygnus.com> <199908120500.PAA30022@tango.anu.edu.au> <19990811224344.A14713@cygnus.com> <199908120707.RAA30438@tango.anu.edu.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <199908120707.RAA30438@tango.anu.edu.au>; from Paul Mackerras on Thu, Aug 12, 1999 at 05:07:02PM +1000 Sender: owner-linuxppc-dev@lists.linuxppc.org List-Id: On Thu, Aug 12, 1999 at 05:07:02PM +1000, Paul Mackerras wrote: > > 10 > > One-cycle access to L1 cache, I guess? No, 2 Cycles to L1 cache. One cycle to execute the store, which merely adds an entry to the store buffer. > > 223 > > Because of i-cache misses, presumably Presumably. The 10 and 94 numbers are all that's interesting. > Interesting. Sounds like each wmb takes about 12 cycles ((94-10)/7), > which sounds a bit like it is going all the way out to the memory bus > and back before the cpu does the next instruction. > > (Ob. nitpicking: if a wmb takes 12 cycles, how come we can do a wmb > and 8 stores in 10 cycles? :-) Because it doesn't work like that. wmb adds a magic token to the store buffer that prevents write combining and other such hw optimizations. Timing stq $31,addr stq $31,addr+8 vs stq $31,addr wmb stq $31,addr+8 shows only 1 cycle difference between the two. I'm not quite sure how the 12 works out. I do know that L2 cache is 12 cycles away, but that may just be coincidence. Going all the way out to the memory bus would take a whole lot longer than 12 cycles. More like 36. > What numbers do you get on alpha if you point it at a framebuffer, > just for interest? I'll give that a try tomorrow. r~ [[ This message was sent via the linuxppc-dev mailing list. Replies are ]] [[ not forced back to the list, so be sure to Cc linuxppc-dev if your ]] [[ reply is of general interest. Please check http://lists.linuxppc.org/ ]] [[ and http://www.linuxppc.org/ for useful information before posting. ]]