From mboxrd@z Thu Jan 1 00:00:00 1970 From: annie li Subject: Re: [Xen-devel] [PATCH net] xen-netback: use jiffies_64 value to calculate credit timeout Date: Mon, 28 Oct 2013 10:58:32 +0800 Message-ID: <526DD2D8.5030405@oracle.com> References: <1382872313-11675-1-git-send-email-wei.liu2@citrix.com> <526DCDB8.1080908@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, Jason Luan To: Wei Liu Return-path: Received: from aserp1040.oracle.com ([141.146.126.69]:47475 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753066Ab3J1C6s (ORCPT ); Sun, 27 Oct 2013 22:58:48 -0400 In-Reply-To: <526DCDB8.1080908@oracle.com> Sender: netdev-owner@vger.kernel.org List-ID: 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; > >> 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