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Date: Fri, 21 Aug 2009 00:00:54 -0400 From: Bill Fink <billfink@...dspring.com> To: Ben Hutchings <bhutchings@...arflare.com> Cc: Aviv Greenberg <avivgnet@...il.com>, Andrew Gallatin <gallatin@...i.com>, netdev@...r.kernel.org Subject: Re: Receive side performance issue with multi-10-GigE and NUMA On Thu, 20 Aug 2009, Ben Hutchings wrote: > On Thu, 2009-08-20 at 03:26 -0400, Bill Fink wrote: > > On Sat, 15 Aug 2009, Aviv Greenberg wrote: > > > > > > There may be something in the chipset > > > > > > shooting in the dark: when you lspci -vvv and check the MaxPayload and > > > MaxReadReq values for the myri devices - what are the values and are > > > they equal? Are they the same on all your platforms? > > > > IIRC, under DevCap they indicated MaxPayload 4096 bytes, and under > > DevCtl they indicated MaxPayload 128 bytes and MaxReadReq 4096 bytes, > > and was the same on both the Asus and SuperMicro systems. I will > > doublecheck tomorrow at work. I am not clear on the meanings of > > the different parameters. And is DevCtl for PCI control messages > > and DevCap for actual data transfers or something else? > > DevCap is the capability register, which is read-only; DevCtl is the > control register which holds the actual settings. > > MaxPayload is the MTU and MRU for PCIe packets. Each sub-tree of > devices connected to a single PCIe root port needs to have MaxPayload > set consistently. MaxReadReq is the maximum size of any DMA read > request. It is a per-device setting (or possibly per-function; I > forget). It can be much larger than MaxPayload since read completions > can be fragmented. Thanks for the explanation. I saw a BIOS setting that allowed increasing the MaxPayload from 128 bytes to 256 bytes, and then verified that an "lspci -vvv" then showed the DevCtl MaxPayload to be 256 bytes. But unfortunately it didn't help improve the read side performance any. -Bill -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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