| Message ID | 1394658281-2488-1-git-send-email-zoltan.kiss@citrix.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, Mar 12, 2014 at 09:04:41PM +0000, Zoltan Kiss wrote: > If there are unconsumed requests in the ring, but there isn't enough free > pending slots, the NAPI instance deschedule itself. As the frontend won't send > any more interrupts in this case, it is the task of whoever release the pending > slots to schedule the NAPI instance in this case. Originally it was done in the > callback, but it's better at the end of the dealloc thread, otherwise there is > a risk that the NAPI instance just deschedule itself as the dealloc thread > couldn't release any used slot yet. However, as there are a lot of pending > packets, NAPI will be scheduled again, and it is very unlikely that the dealloc > thread can't release enough slots in the meantime. > So this patch restores the property that "only two parties access the ring", right? Wei. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 2014-03-13 at 10:17 +0000, Wei Liu wrote: > On Wed, Mar 12, 2014 at 09:04:41PM +0000, Zoltan Kiss wrote: > > If there are unconsumed requests in the ring, but there isn't enough free > > pending slots, the NAPI instance deschedule itself. As the frontend won't send > > any more interrupts in this case, it is the task of whoever release the pending > > slots to schedule the NAPI instance in this case. Originally it was done in the > > callback, but it's better at the end of the dealloc thread, otherwise there is > > a risk that the NAPI instance just deschedule itself as the dealloc thread > > couldn't release any used slot yet. However, as there are a lot of pending > > packets, NAPI will be scheduled again, and it is very unlikely that the dealloc > > thread can't release enough slots in the meantime. > > > > So this patch restores the property that "only two parties access the > ring", right? I think so, and therefore: Acked-by: Ian Campbell <ian.campbell@citrix.com> Ian. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 13/03/14 10:42, Ian Campbell wrote: > On Thu, 2014-03-13 at 10:17 +0000, Wei Liu wrote: >> On Wed, Mar 12, 2014 at 09:04:41PM +0000, Zoltan Kiss wrote: >>> If there are unconsumed requests in the ring, but there isn't enough free >>> pending slots, the NAPI instance deschedule itself. As the frontend won't send >>> any more interrupts in this case, it is the task of whoever release the pending >>> slots to schedule the NAPI instance in this case. Originally it was done in the >>> callback, but it's better at the end of the dealloc thread, otherwise there is >>> a risk that the NAPI instance just deschedule itself as the dealloc thread >>> couldn't release any used slot yet. However, as there are a lot of pending >>> packets, NAPI will be scheduled again, and it is very unlikely that the dealloc >>> thread can't release enough slots in the meantime. >>> >> >> So this patch restores the property that "only two parties access the >> ring", right? > > I think so, and therefore: > Acked-by: Ian Campbell <ian.campbell@citrix.com> I've just discussed this with Ian, this solution still doesn't solve the racing between NAPI and the dealloc thread, however it only causes some unnecessary napi_schedule's, not ring stalls. There is a better solution, I'll post it as soon as it passes all the test! Zoli -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Zoltan Kiss <zoltan.kiss@citrix.com> Date: Thu, 13 Mar 2014 15:44:37 +0000 > I've just discussed this with Ian, this solution still doesn't solve > the racing between NAPI and the dealloc thread, however it only causes > some unnecessary napi_schedule's, not ring stalls. > There is a better solution, I'll post it as soon as it passes all the > test! Ok, I'm skipping this patch therefore. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c index eae9724..07c9677 100644 --- a/drivers/net/xen-netback/netback.c +++ b/drivers/net/xen-netback/netback.c @@ -1516,13 +1516,6 @@ void xenvif_zerocopy_callback(struct ubuf_info *ubuf, bool zerocopy_success) wake_up(&vif->dealloc_wq); spin_unlock_irqrestore(&vif->callback_lock, flags); - if (RING_HAS_UNCONSUMED_REQUESTS(&vif->tx) && - xenvif_tx_pending_slots_available(vif)) { - local_bh_disable(); - napi_schedule(&vif->napi); - local_bh_enable(); - } - if (likely(zerocopy_success)) vif->tx_zerocopy_success++; else @@ -1594,6 +1587,13 @@ static inline void xenvif_tx_dealloc_action(struct xenvif *vif) for (i = 0; i < gop - vif->tx_unmap_ops; ++i) xenvif_idx_release(vif, pending_idx_release[i], XEN_NETIF_RSP_OKAY); + + if (RING_HAS_UNCONSUMED_REQUESTS(&vif->tx) && + xenvif_tx_pending_slots_available(vif)) { + local_bh_disable(); + napi_schedule(&vif->napi); + local_bh_enable(); + } }
If there are unconsumed requests in the ring, but there isn't enough free pending slots, the NAPI instance deschedule itself. As the frontend won't send any more interrupts in this case, it is the task of whoever release the pending slots to schedule the NAPI instance in this case. Originally it was done in the callback, but it's better at the end of the dealloc thread, otherwise there is a risk that the NAPI instance just deschedule itself as the dealloc thread couldn't release any used slot yet. However, as there are a lot of pending packets, NAPI will be scheduled again, and it is very unlikely that the dealloc thread can't release enough slots in the meantime. Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com> --- -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html