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Date: Tue, 29 Sep 2009 09:54:16 +0200 From: "Lennart Baruschka" <FunFlyer@....net> To: Alan Cox <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org Subject: Re: Disabling DMA with ICH10? Hi, On Mon, 2009-09-28 at 23:40 +0100, Alan Cox wrote: > > 2. My system uses an ICH10 chipset, the harddrive is connected to the > > Intel SATA controller. Is there a way to disable DMA and switch back to > > PIO? I tried compiling with libata support and without SCSI support, but > > the kernel is unable to mount root (no matter if /dev/sda1 > > or /dev/hda1), then. > > If you disable DMA you will make your performance and latency worse not > better as the PIO transfers will stall the bus and thus the processor. I thought that PIO transfers (which I understand to be write32()/read32()'s) unlike DMA transfers could be interrupted by an high-priority interrupt. Is that wrong? > If you really are that latency sensitive then the more normal approach > would be to lock one core for real time use, load the critical code into > that core CPU cache and run from cache. If you are utterly pushing the > limit you might even do crazy stuff like use on thread on the core to > execute RT stuff and the other to issue any I/O accesses that might stall. Actually, that's what I do - except for locking the page, yet. I do need to access the PCI bus in real time, though. So I wonder what happens when the RT CPU is getting data from the PCI device, doing some calculations on it and then writing back some data to the device, __while at the same time__ another (non-RT) CPU starts a DMA transfer. I figured the DMA would block the PCI bus, having my interrupt wait for it to finish. That's why I'm trying to avoid DMA. Please let me know at what point I am mistaken. Cheers Lennart -- Jetzt kostenlos herunterladen: Internet Explorer 8 und Mozilla Firefox 3.5 - sicherer, schneller und einfacher! http://portal.gmx.net/de/go/atbrowser -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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