Subject: Re: [Ksummit-2005-discuss] Summary of 2005 Kernel Summit Proposed Topics

From: Mike Christie <[email-masked]>
Date: Sun, 27 Mar 2005 10:26:29 -0800

Dmitry Yusupov wrote:
> On Sat, 2005-03-26 at 23:57 -0800, David S. Miller wrote:
> 
>>On Sat, 26 Mar 2005 23:05:30 -0800
>>Dmitry Yusupov <[email-masked]> wrote:
>>
>>
>>>>During these gaps in time, you will need to keep your HW receive
>>>>ring populated with packets.
>>>
>>>ethernet flow-control must take care this case.
>>>
>>>If driver's replenish logic could mix alloc_skb/netif_rx and SKB
>>>recycling than pause frames should never happen even with gige+
>>>interfaces.
>>
>>I don't see what the big deal is if pause frames
>>are generated when the system is low on atomic memory
>>and RX allocations thus fail.
> 
> 
> not a big deal may be. but. very interesting case when OOM causing
> paging in/out and swapping device are on the same network under iSCSI
> control. (disk-less setups) having reliable receive in that case is
> important for making progress for READ operations.

reliable receive is ciritical for WRITEs. Even if the WRITE is executed
successfully on the remote device, if we cannot receive the return status
from the device the operation will fail at the iscsi driver side due to a
SCSI timeout.

> 
> 
>>SKB recycling doesn't get the user on the cpu faster
>>to receive the data.  I don't understand how you expect
>>the recycling to be guarenteed except perhaps as a special
>>case for iSCSI taking in the TCP packets in the ->data_ready()
>>callback.  In that case it's exactly that, a special case
>>hack, and not something generically useful at all.
> 
> 
> right. this is what Open-iSCSI project is using for READs.
>