Hi, I think that the problem is caused by ehci driver instead of ARM SMP scheduler, and I have verified that patch below can fix the problem. And the patch has been posted on usb/arm/omap mail list for discussion.
But I am wondering that why no such problem after passing 'nosmp' to kernel. >From d85a08714ed23ec8688013b464dc90c6386db0d8 Mon Sep 17 00:00:00 2001 From: Ming Lei <ming....@canonical.com> Date: Sat, 27 Aug 2011 22:29:15 +0800 Subject: [PATCH] usb: ehci: fix update qtd->token in qh_append_tds This patch fixs one performance bug on ARM Cortex A9 dual core platform, which has been reported on quite a few ARM machines(OMAP4, Tegra 2, snowball...), see details from link of https://bugs.launchpad.net/bugs/709245. In fact, one mb() on ARM is enough to flush L2 cache, but 'dummy->hw_token = token;' after mb() is added just for obeying correct mb() usage. The patch has been tested ok on OMAP4 panda A1 board, the performance of 'dd' over usb mass storage can be increased from 4~5MB/sec to 14~16MB/sec after applying this patch. Signed-off-by: Ming Lei <ming....@canonical.com> --- drivers/usb/host/ehci-q.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-) diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c index 0917e3a..65b5021 100644 --- a/drivers/usb/host/ehci-q.c +++ b/drivers/usb/host/ehci-q.c @@ -1082,6 +1082,20 @@ static struct ehci_qh *qh_append_tds ( wmb (); dummy->hw_token = token; + /* The mb() below is added to make sure that + * 'token' can be writen into qtd, so that ehci + * HC can see the up-to-date qtd descriptor. On + * some archs(at least on ARM Cortex A9 dual core), + * writing into coherenet memory doesn't mean the + * value written can reach physical memory + * immediately, and the value may be buffered + * inside L2 cache. 'dummy->hw_token = token;' + * after mb() is added for obeying correct mb() + * usage. + * */ + mb(); + token = dummy->hw_token; + urb->hcpriv = qh_get (qh); } } -- 1.7.4.1 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/709245 Title: ARM SMP scheduler performance bug To manage notifications about this bug go to: https://bugs.launchpad.net/linaro-ubuntu/+bug/709245/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
