LKML Archive on
help / color / mirror / Atom feed
From: Haiyang Zhang <>
To: Jason Wang <>
Cc: "" <>,
	"" <>,
	KY Srinivasan <>,
	"" <>,
	"" <>,
Subject: RE: [PATCH net] hyperv: Fix the error processing in netvsc_send()
Date: Wed, 4 Feb 2015 22:26:51 +0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 2850 bytes --]

> -----Original Message-----
> From: Jason Wang []
> Sent: Wednesday, February 4, 2015 2:29 AM
> > The EAGAIN error doesn't normally happen, because we set the hi water
> > mark
> > to stop send queue.
> This is not true since only txq was stopped which means only network
> stack stop sending packets but not for control path e.g
> rndis_filter_send_request() or other callers who call
> vmbus_sendpacket() directly (e.g recv completion).
> For control path, user may meet several errors when they want to change
> mac address under heavy load.
> What's more serious is netvsc_send_recv_completion(), it can not even
> recover from more than 3 times of EAGAIN.
> I must say mixing data packets with control packets with the same
> channel sounds really scary. Since control packets could be blocked or
> even dropped because of data packets already queued during heavy load,
> and you need to synchronize two paths carefully (e.g I didn't see any
> tx lock were held if rndis_filter_send_request() call netsc_send()
> which may stop or start a queue).

The RING_AVAIL_PERCENT_HIWATER is defined to be 20, so the data traffic
can only occupy 20% of the ring buffer before stopping the txq. So, this
mechanism ensures the control messages are not blocked by data traffic.

> >  If in really rare case, the ring buffer is full and there
> > is no outstanding sends, we can't stop queue here because there will
> > be no
> > send-completion msg to wake it up.
> Confused, I believe only txq is stopped but we may still get completion
> interrupt in this case.

If there is no outstanding sends in this queue (queue_sends[q_idx]), we 
won't receive any more send-completion msg.

> > And, the ring buffer is likely to be
> > occupied by other special msg, e.g. receive-completion msg (not a
> > normal case),
> > so we can't assume there are available slots.
> Then why not checking hv_ringbuf_avail_percent() instead? And there's
> no need to check queue_sends since it does not count recv completion.

When ret == -EAGAIN, which means the ring is full, we don't need to check

> > We don't request retry from
> > the upper layer in this case to avoid possible busy retry.
> Can't we just do this by stopping txq and depending on tx interrupt to
> wake it?

There is no tx interrupt. Do you mean rx interrupt for the send-completion?

In usual cases, when we hit the high water mark, the stopped queue depends on
the send-completion msg to wake up. But, not in some special cases.
As said above, we won't receive any more send-completion msg when there is 
no outstanding sends in this queue.

- Haiyang


  reply	other threads:[~2015-02-04 22:41 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-29 20:34 Haiyang Zhang
2015-01-30 10:25 ` Jason Wang
2015-01-30 15:05   ` Haiyang Zhang
     [not found]     ` <>
2015-02-02  6:49       ` Jason Wang
2015-02-03 15:46         ` Haiyang Zhang
     [not found]           ` <>
2015-02-04  7:29             ` Jason Wang
2015-02-04 22:26               ` Haiyang Zhang [this message]
2015-02-01  1:32 ` David Miller

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \
    --subject='RE: [PATCH net] hyperv: Fix the error processing in netvsc_send()' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).