RE: [PATCH 2.6.24]S2io: Default to IntA interrupt type when there are less than 4 CPUs in the system.

We had found during performance measurement/analysis that with 2 cpus
and napi disabled, and the system transmitting (tcp), the cpus get too
busy due to receive interrupt handling, reducing performance by around
10%.
 
But then again, when the number of cpus increase, the interrupt scaling
is much better and msi-x gives better numbers.

We are modifying the driver to enable napi with msi-x, but this work is
in progress and may get released in a few months. 

The Xframe hardware has 8 independent dma channels for transmit and
receive, with doorbells for each channel. Multiple channels are in use
for a single netdev. In one of the variations of this driver that is not
released to netdev, the received packets are steered to a channel based
on hashing on a preconfigured criteria such as sockets on tcp_ipv4,
udp_ipv4, tcp_ipv6, udp_ipv6 or addresses in ipv4/6. The transmits are
handled in a similar manner. 

The current napi implementation looks like  -
driver_poll(struct net_device *dev, int *budget)

where as, something like -
driver_poll(struct context *context, int *budget)

would be ideal for hardware like ours. Each channel could schedule a
respective poller, rather than the current method which requires
synchronization between the poller and the channels.

Ram

-----Original Message-----
From: Jeff Garzik [mailto:jeff@garzik.org]
Sent: Friday, August 10, 2007 10:39 AM
To: Rick Jones
Cc: Sivakumar Subramani; netdev@vger.kernel.org; support
Subject: Re: [PATCH 2.6.24]S2io: Default to IntA interrupt type when

there

are less than 4 CPUs in the system.

Rick Jones wrote:

quoted

Sivakumar Subramani wrote:

quoted

- Default to IntA interrupt type when there are less than 4 CPUs in
the system.

It might be good to include _why_ in the comment(s).  I certainly am
curious to know the reason, and it would be good to have in there

for

quoted

"posterity" should the underlying conditions change.

Indeed.  I really want to know 'why'?

	Jeff