From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <04c347e8d648750d2e5c10d133a878b9@quintile.net> From: "Steve Simon" Date: Sun, 30 Apr 2006 19:12:03 +0100 To: 9fans@cse.psu.edu Subject: Re: [9fans] nvidia scrolling performance In-Reply-To: <41e3f50fc059ce546b4855ecfc3bd8ef@swtch.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Topicbox-Message-UUID: 4b57e958-ead1-11e9-9d60-3106f5b1d025 > Frame buffer memory is very very slow to read from, > and not just on nvidia. When I did some timings six years > ago, I found that reading from frame buffer memory > was slower than reading from disk. I'm sure the situation > hasn't gotten better. It's not on the fast path for any > other system, so the vendors just don't care. I may be talking rubbish but I understood this is a fundamental problem with reading VGA memory over the PCI bus. VGA cards are designed for fast writes and not fast reads. People have been very interested in using the GCPUs in graphics cards to do video processing (to disk rather than for display) but the limiting factor seems to have been the speed at which data can be read back. I do hear that some cards are appearing with dual PCIX which will allow symetric access speeds to the frame buffer. -Steve