On Thu, Oct 18, 2012 at 1:48 PM, Felix Fietkau <[email protected]> wrote:
> On 2012-10-18 10:44 PM, Tim Harvey wrote: > > There are 2 target's affected - I figured it belonged in a global area. > > I only have the cns3xxx target. If you feel this should be changed I'll > > re-submit it for just that target. > That doesn't explain why you want to add a configuration option for it. > Who would want to configure this instead of only having a sane default. > > - Felix > > I'm not saying enabling L2X0 is not 'sane', I just want to provide the user a way to optionally disable it. If your asking why, I thought I explained it well enough in the description of the option in Config.in. If you want some performance numbers to back it up I took at GW2388 (600MHz dual-core ARM11 cns3xxx) with OpenWrt trunk on it and configured it for 'bridging' (low CPU overhead, high I/O overhead). Using iperf I tested TCP performance and found a 63% improvement in performance with L2X0 disabled. Testing gzip showed a 58% decrease in performance with L2X0 disabled. With I/O bound operations the benefit of L2X0 does not outweigh the cost (setting up DMA etc) as there is little cache thrashing. With CPU/memory bound operations the benefit of L2X0 is worth the cost. Many of our customers use our boards in scenarios where L2X0 disabled provides the best performance. I would rather have a nice clean openwrt .config for this rather than have them hack at target/linux/cns3xxx/config-3.3. Please explain if you think I'm going about this completely wrong. Thanks, Tim
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