From: annie li <annie.li@oracle•com>
To: Wei Liu <wei.liu2@citrix•com>
Cc: Ian Campbell <ian.campbell@citrix•com>,
netdev@vger•kernel.org, xen-devel@lists•xen.org,
david.vrabel@citrix•com, jbeulich@suse•com,
Jason Luan <jianhai.luan@oracle•com>
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 [thread overview]
Message-ID: <526DD2D8.5030405@oracle.com> (raw)
In-Reply-To: <526DCDB8.1080908@oracle.com>
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 <jbeulich@suse•com>
>> Suggested-by: David Vrabel <david.vrabel@citrix•com>
>> 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 */
>> + 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
next prev parent reply other threads:[~2013-10-28 2:58 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 ` annie li [this message]
2013-10-28 6:28 ` [Xen-devel] " jianhai luan
2013-10-28 11:30 ` Wei Liu
2013-10-28 8:21 ` David Vrabel
2013-10-28 8:36 ` [Xen-devel] " jianhai luan
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