From mboxrd@z Thu Jan 1 00:00:00 1970 From: jianhai luan Subject: Re: [Xen-devel] [PATCH net] xen-netback: use jiffies_64 value to calculate credit timeout Date: Mon, 28 Oct 2013 14:28:28 +0800 Message-ID: <526E040C.6060802@oracle.com> References: <1382872313-11675-1-git-send-email-wei.liu2@citrix.com> <526DCDB8.1080908@oracle.com> <526DD2D8.5030405@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Ian Campbell , netdev@vger.kernel.org, xen-devel@lists.xen.org, david.vrabel@citrix.com, jbeulich@suse.com To: annie li , Wei Liu Return-path: Received: from userp1040.oracle.com ([156.151.31.81]:42599 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755548Ab3J1G2t (ORCPT ); Mon, 28 Oct 2013 02:28:49 -0400 In-Reply-To: <526DD2D8.5030405@oracle.com> Sender: netdev-owner@vger.kernel.org List-ID: On 2013-10-28 10:58, annie li wrote: > > On 2013-10-28 10:36, annie li wrote: >> >> On 2013-10-27 19:11, Wei Liu wrote: >>> time_after_eq() only works if the delta is < MAX_ULONG/2. >>> >>> For a 32bit Dom0, if netfront sends packets at a very low rate, the >>> time >>> between subsequent calls to tx_credit_exceeded() may exceed MAX_ULONG/2 >>> and the test for timer_after_eq() will be incorrect. Credit will not be >>> replenished and the guest may become unable to send packets (e.g., if >>> prior to the long gap, all credit was exhausted). >>> >>> Use jiffies_64 variant to mitigate this problem for 32bit Dom0. >>> >>> Suggested-by: Jan Beulich >>> Suggested-by: David Vrabel >>> Signed-off-by: Wei Liu >>> Cc: Ian Campbell >>> Cc: Jason Luan >>> --- >>> drivers/net/xen-netback/common.h | 1 + >>> drivers/net/xen-netback/interface.c | 4 ++-- >>> drivers/net/xen-netback/netback.c | 13 ++++++------- >>> 3 files changed, 9 insertions(+), 9 deletions(-) >>> >>> diff --git a/drivers/net/xen-netback/common.h >>> b/drivers/net/xen-netback/common.h >>> index 5715318..400fea1 100644 >>> --- a/drivers/net/xen-netback/common.h >>> +++ b/drivers/net/xen-netback/common.h >>> @@ -163,6 +163,7 @@ struct xenvif { >>> unsigned long credit_usec; >>> unsigned long remaining_credit; >>> struct timer_list credit_timeout; >>> + u64 credit_window_start; >>> /* Statistics */ >>> unsigned long rx_gso_checksum_fixup; >>> diff --git a/drivers/net/xen-netback/interface.c >>> b/drivers/net/xen-netback/interface.c >>> index 01bb854..8c45b63 100644 >>> --- a/drivers/net/xen-netback/interface.c >>> +++ b/drivers/net/xen-netback/interface.c >>> @@ -312,8 +312,8 @@ struct xenvif *xenvif_alloc(struct device >>> *parent, domid_t domid, >>> vif->credit_bytes = vif->remaining_credit = ~0UL; >>> vif->credit_usec = 0UL; >>> init_timer(&vif->credit_timeout); >>> - /* Initialize 'expires' now: it's used to track the credit >>> window. */ >>> - vif->credit_timeout.expires = jiffies; >>> + /* credit window is tracked in credit_window_start */ >>> + vif->credit_window_start = get_jiffies_64(); >>> dev->netdev_ops = &xenvif_netdev_ops; >>> dev->hw_features = NETIF_F_SG | NETIF_F_IP_CSUM | NETIF_F_TSO; >>> diff --git a/drivers/net/xen-netback/netback.c >>> b/drivers/net/xen-netback/netback.c >>> index f3e591c..1bc0688 100644 >>> --- a/drivers/net/xen-netback/netback.c >>> +++ b/drivers/net/xen-netback/netback.c >>> @@ -1185,18 +1185,17 @@ out: >>> static bool tx_credit_exceeded(struct xenvif *vif, unsigned size) >>> { >>> - unsigned long now = jiffies; >>> - unsigned long next_credit = >>> - vif->credit_timeout.expires + >>> - msecs_to_jiffies(vif->credit_usec / 1000); >>> + u64 now = get_jiffies_64(); >>> + u64 next_credit = vif->credit_window_start + >>> + (u64)msecs_to_jiffies(vif->credit_usec / 1000); >> >> You simply replace "credit_timeout.expires" with >> "vif->credit_window_start" here, and never update >> "vif->credit_window_start" in following code. >> >>> /* Timer could already be pending in rare cases. */ >>> if (timer_pending(&vif->credit_timeout)) >>> return true; >>> /* Passed the point where we can replenish credit? */ >>> - if (time_after_eq(now, next_credit)) { >>> - vif->credit_timeout.expires = now; >>> + if (time_after_eq64(now, next_credit)) { >>> + vif->credit_timeout.expires = (unsigned long)now; >> >> updates credit_window_start as following, >> vif->credit_window_start = (unsigned long)now; > > both credit_window_start and credit_timeout.expires need to be updated > here, > > vif->credit_window_start = (unsigned long)now; > vif->credit_timeout.expires = (unsigned long)now; Annie should be correct. It is good to me but i afraid that get_jiffies_64() and time_after_eq64() will bring some performance's load when transmit is busy in 32bit. I will do some test about the patch. No matter what, i prefer own patch. Thanks, Jason > >> >>> tx_add_credit(vif); >>> } >>> @@ -1207,7 +1206,7 @@ static bool tx_credit_exceeded(struct xenvif >>> *vif, unsigned size) >>> vif->credit_timeout.function = >>> tx_credit_callback; >>> mod_timer(&vif->credit_timeout, >>> - next_credit); >>> + (unsigned long)next_credit); >> >> vif->credit_timeout.expires is unsigned long, and this still causes >> original issue on 32bit system, which works well on 64bit. Or >> rewriting code to avoid uses of vif->credit_timeout.expires, but it >> is complex. > My understanding here is wrong, please ignore this. > > Thanks > Annie