Date: Sun, 03 May 1998 19:57:18 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: John Hay <jhay@mikom.csir.co.za> Cc: freebsd-bugs@FreeBSD.ORG Subject: Re: i386/5398 Message-ID: <11869.894218238@critter.freebsd.dk> In-Reply-To: Your message of "Sat, 03 May 1998 19:49:22 %2B0200." <199805031749.TAA07478@zibbi.mikom.csir.co.za>
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In message <199805031749.TAA07478@zibbi.mikom.csir.co.za>, John Hay writes: >> > How is XFree86, a userland program, able to disable interrupts ? >> > The Hardware blitter/PCI latency also seems impossible, 115200 = >> > 11.5 KBytes/sec = 86uS per character x the FIFO depth (after the hack) >> > of 4 or 8 character times is over 500uS. It just doesn't make any >> > sense. >> >> By monopolizing the PCI bus, while blitting 3 or 4 MB data, I can >> certainly see PCI starvation. Remeber that to blt 3 MB around, you >> have to read 3 MB and write 3MB, so that is 6MB over a 133MB/sec bus, >> giving a minimum duration of 45 msec per blt. > >Just to get my understanding of the hardware a little better. Is this >blitting just doing something like a software memory copy, like what >the C function bcopy() does? And can that really block interrupts just >because it is done over the PCI bus? Or does blitting use something >different? I don't know how it is done exactly, check with XFree86. I just know that any PCI bus hogging will send your interrupt latency soaring :-( -- Poul-Henning Kamp FreeBSD coreteam member phk@FreeBSD.ORG "Real hackers run -current on their laptop." "ttyv0" -- What UNIX calls a $20K state-of-the-art, 3D, hi-res color terminal To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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