-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Am Sunday 31 August 2003 16:20 schrieb Jon Burgess: > I see that you've recently written this patch on the subject: > > * stream. By changing this parameter, the PCI burst mode for DMA 3 can be > * optimised. The 3 least significant bits of "budget_burst" equal bursts > * of 1,2,4,8,16,32,64 and 128 Dwords. The fourth and fifth bit are assigned > * to the FIFO threshold: 4,8,16 or 32 Dwords. The default is 0x1c: 16 DW > * burst and 32 DW FIFO. > *************************************************************************** >*/ int budget_burst = 0x1c; > > I think what you've written is wrong, my interpretation of the datasheet > is as follows: > - bits 0,1 control the threshold. > - bits 2,3,4 control the burst size. > This makes the 0x1c == 0001 1100 is > Threshold(00) == 4 Dwords > Burst(111) == 128Dwords > > I think the default FIFO threshold seems too aggressive. I think this > basically makes the SAA7146 request access to the PCI bus almost > continuously which I think it leads to the transfers on the bus being > unneccessarily small which drops the efficiency and therefore overall > bandwidth on the PCI bus. > > Your recommended setting of 0x03 == 0000 0011 > Threshold(11) = 32 Dwords > Burst(000) = 1 Dword > > My impression is that a high threshold helps. Could you try increasing > the burst size as well? The only thing this should do is improve the > efficiency of the bus. > > Given that anecdotal evidence that higher speed CPU's have more problems > than slow CPU's, perhaps what is happening is that by reducing the bus > efficiency you've efectively slowed the accesses by the CPU and this > only indirectly avoids the problem and doesn't actually fix it.
Oh my god, you are right, I should read the docs more carefully ;-) But it doesn't matter, because I have tested all combinations and when I interpret them now, I see optimal results for high threshold and 1 Dword burst. When I increase to 2 Dwords burst I get immediatly a bad stream. Decreasing the threshold also decreases the stream quality, but with less noticable effects until I reach 4 Dwords threshold and a bad stream. Regarding the PCI bus, I have also a 845 chipset, but without integrated graphics. My slots are filled with a normal AGP card, a Nova-S, an em8300 and a wireless network card. I have already pulled out em8300 and WiFi card, but it changed nothing. I don't know what internal PCI devices can load the bus, USB 2.0 gets into my mind, but there are only USB 1.0 devices plugged in. The hard drive is also idle. I am running out of ideas... I will investigate the IRQ issue this evening. I am pretty sure that your patch is executed half of time, because I inserted a syslog message inside your if statement and in a newly created else statement another message. They alternated in the log most of the time, I am just not sure about the absolute IRQ/s. bye, Stefan -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.2 (GNU/Linux) iD8DBQE/Uw4b/bI7T1LKTh8RAm7xAKCPZ391bSdLmDsFlOHNB1YXTSssLACfTzIk oRHZlvKs9IJHob9zf4SEdLM= =zXmz -----END PGP SIGNATURE----- -- Info: To unsubscribe send a mail to [EMAIL PROTECTED] with "unsubscribe linux-dvb" as subject.
