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[Xen-users] Fwd: Pls help: netfront tx ring frozen (any clues appreciated)

---------- Forwarded message ----------
From: Vijay Chander <vijay.chander@xxxxxxxxx>
Date: Sat, Feb 25, 2012 at 7:46 AM
Subject: Re: Pls help: netfront tx ring frozen (any clues appreciated)
To: xen-devel@xxxxxxxxxxxxxxxxxxx

If anybody encountered a similar situation as below where the netfront TX ring is stuck ,
can you pls provide some pointers on how to get around this problem ?

This typically happens after about 2days of overnight traffic tests.


On Thu, Feb 23, 2012 at 8:29 AM, Vijay Chander <vijay.chander@xxxxxxxxx> wrote:

    We are running into a situation where rsp_prod index in the shared ring is not getting updated
for the netfront tx ring by the netback.

    We see that rsp_cons is the same value as rsp_prod, with req_prod 236 slots away(tx ring is full). 
From looking at the netfront driver code, it looks as if xennet_tx_buf_gc processing only happens if rsp_prod is more 
than rsp_cons.

   Our understanding is that netfront sets rsp_cons to tell the netback to start processing transmits
from rsp_cons index onwards till req_prod. Once netback is done process X requests, it will increment rsp_prod
by X. This will cause netfront to look at the status of each of individual responses for the slots starting
from rsp_cons till rsp_prod (with rsp_prod  - rsp_cons = X in this case).

   Is there anyway to workaround this ? Will xennet_disconnect_backend(), xennet_connect()
on the netfront cause us to recover from this stuck situation. We are ok with pending TX packets getting dropped
since we have TCP running on top.


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