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

To: open-iscsi@xxxxxxxxxxxxxxxx
Subject: Re: [Ksummit-2005-discuss] Summary of 2005 Kernel Summit Proposed Topics
From: Mike Christie <michaelc@xxxxxxxxxxx>
Date: Sun, 27 Mar 2005 10:26:29 -0800
Cc: mpm@xxxxxxxxxxx, andrea@xxxxxxx, James.Bottomley@xxxxxxxxxxxxxxxxxxxxx, ksummit-2005-discuss@xxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <1111911493.5824.12.camel@mylaptop>
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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 <dmitry_yus@xxxxxxxxx> 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.



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