[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Load increase after memory upgrade (part2)
On Wed, Dec 14, 2011 at 04:23:51PM -0400, Konrad Rzeszutek Wilk wrote: > On Mon, Dec 05, 2011 at 10:26:21PM -0500, Konrad Rzeszutek Wilk wrote: > > On Sun, Dec 04, 2011 at 01:09:28PM +0100, Carsten Schiers wrote: > > > Here with two cards enabled and creating a bit "work" by watching TV with > > > one oft hem: > > > > > > [ 23.842720] Starting SWIOTLB debug thread. > > > [ 23.842750] swiotlb_start_thread: Go! > > > [ 23.842838] xen_swiotlb_start_thread: Go! > > > [ 28.841451] 0 [budget_av 0000:00:01.0] bounce: from:435596(slow:0)to:0 > > > map:658 unmap:0 sync:435596 > > > [ 28.841592] SWIOTLB is 4% full > > > [ 33.840147] 0 [budget_av 0000:00:01.0] bounce: from:127652(slow:0)to:0 > > > map:0 unmap:0 sync:127652 > > > [ 33.840283] SWIOTLB is 4% full > > > [ 33.844222] 0 budget_av 0000:00:01.0 alloc coherent: 8, free: 0 > > > [ 38.840227] 0 [budget_av 0000:00:01.0] bounce: from:128310(slow:0)to:0 > > > map:0 unmap:0 sync:128310 > > > > Whoa. Yes. You are definitly using the bounce buffer :-) > > > > Now it is time to look at why the drive is not using those coherent ones - > > it > > looks to allocate just eight of them but does not use them.. Unless it is > > using them _and_ bouncing them (which would be odd). > > > > And BTW, you can lower your 'swiotlb=XX' value. The 4% is how much you > > are using of the default size. > > So I able to see this with an atl1c ethernet driver on my SandyBridge i3 > box. It looks as if the card is truly 32-bit so on a box with 8GB it > bounces the data. If I booted the Xen hypervisor with 'mem=4GB' I get no > bounces (no surprise there). > > In other words - I see the same behavior you are seeing. Now off to: > > > > I should find out_why_ the old Xen kernels do not use the bounce buffer > > so much... > > which will require some fiddling around. And I am not seeing any difference - the swiotlb is used with the same usage when booting a classic (old style XEnoLinux) 2.6.32 vs using a brand new pvops (3.2). Obviously if I limit the physical amount of memory (so 'mem=4GB' on Xen hypervisor line), the bounce usage disappears. Hmm, I wonder if there is a nice way to tell the hypervisor - hey, please stuff dom0 under 4GB. Here is the patch I used against classic XenLinux. Any chance you could run it with your classis guests and see what numbers you get? Attachment:
swiotlb-against-old-type.patch _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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