From: David Vrabel <dvrabel@cantab•net>
To: Wei Liu <wei.liu2@citrix•com>,
xen-devel@lists•xen.org, netdev@vger•kernel.org
Cc: Jason Luan <jianhai.luan@oracle•com>,
annie.li@oracle•com, Ian Campbell <ian.campbell@citrix•com>,
jbeulich@suse•com, david.vrabel@citrix•com
Subject: Re: [PATCH net] xen-netback: use jiffies_64 value to calculate credit timeout
Date: Mon, 28 Oct 2013 08:21:43 +0000 [thread overview]
Message-ID: <526E1E97.7090804@cantab.net> (raw)
In-Reply-To: <1382872313-11675-1-git-send-email-wei.liu2@citrix.com>
On 27/10/2013 11:11, 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.
Thanks.
> Suggested-by: Jan Beulich <jbeulich@suse•com>
> Suggested-by: David Vrabel <david.vrabel@citrix•com>
Jan's suggestion; I just agreed with him.
> Signed-off-by: Wei Liu <wei.liu2@citrix•com>
> Cc: Ian Campbell <ian.campbell@citrix•com>
> Cc: Jason Luan <jianhai.luan@oracle•com>
> ---
> 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 */
You could drop this comment as the field name makes this obvious.
> + 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);
>
> /* 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;
Need to set vif->credit_window_start = now here instead of .expires.
> 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);
Need to set vif->credit_window_start = next_credit here as well.
David
next prev parent reply other threads:[~2013-10-28 8:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-27 11:11 [PATCH net] xen-netback: use jiffies_64 value to calculate credit timeout Wei Liu
2013-10-28 2:36 ` annie li
2013-10-28 2:58 ` [Xen-devel] " annie li
2013-10-28 6:28 ` jianhai luan
2013-10-28 11:30 ` Wei Liu
2013-10-28 8:21 ` David Vrabel [this message]
2013-10-28 8:36 ` jianhai luan
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