On 2012-10-19 12:18 AM, Tim Harvey wrote: > On Thu, Oct 18, 2012 at 1:48 PM, Felix Fietkau <[email protected] > <mailto:[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. OK, these differences are much bigger than I expected. However, from the looks of how the code works, it should be easy to add a kernel command line option for either enabling or disabling the l2x0 cache controller. I think this is a lot more useful than choosing l2x0 support at compile-time. It would allow the default builds to properly cover more usage scenarios.
- Felix _______________________________________________ openwrt-devel mailing list [email protected] https://lists.openwrt.org/mailman/listinfo/openwrt-devel
