Messages in this thread | | | From | Anup Patel <> | Date | Thu, 5 Dec 2019 05:16:00 +0530 | Subject | Re: [GIT PULL] Second set of RISC-V updates for v5.5-rc1 |
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On Thu, Dec 5, 2019 at 1:20 AM Alistair Francis <Alistair.Francis@wdc.com> wrote: > > On Wed, 2019-12-04 at 11:38 -0800, Paul Walmsley wrote: > > Alistair, Anup, > > > > On Wed, 4 Dec 2019, Alistair Francis wrote: > > > > > On Wed, 2019-12-04 at 18:22 +0530, Anup Patel wrote: > > > > > > > I had commented on your patch but my comments are still > > > > not addressed. > > > > > > > > Various debug options enabled by this patch have performance > > > > impact. Instead of enabling these debug options in primary > > > > defconfigs, I suggest to have separate debug defconfigs with > > > > these options enabled. > > > > > > +1 > > > > > > OE uses the defconfig (as I'm sure other distros do) and slowing > > > down > > > users seems like a bad idea. > > > > While I respect your points of view, our defconfigs are oriented > > towards > > kernel developers. This is particularly important when right now the > > only > > That is just not what happens though. > > It is too much to expect every distro to maintain a defconfig for RISC- > V. There are constantly new features that need to be enabled/disabled > in the configs and it isn't always clear to outsiders. Which is why we > currently use the defconfig as a base and apply extra features that > distro want on top. > > Expecting every distro to have a kernel developers level of knowledge > about configuring Kconfigs is just unrealistic. > > > RISC-V hardware on the market are test chips. Our expectation is > > that > > Treating RISC-V as a test architecture seems like a good way to make > sure that is all it ever is. > > > distros and benchmarkers will create their own Kconfigs for their > > needs. > > Like I said, that isn't true. After this patch is applied (and it makes > it to a release) all OE users will now have a slower RISC-V kernel. > This also applies to buildroot and probably other distos. > > Now image some company wants to investigate using a RISC-V chip for > their embedded project. They use OE/buildroot to build a quick test > setup and boot Linux. It now runs significantly slower then some other > architecture and they don't choose RISC-V. > > Slowing down all users to help kernel developers debug seems like the > wrong direction. Kernel developers should know enough to be able to > turn on the required configs, why does this need to be the default?
I quickly tried hackbench on SiFive Unleashed board with latest Linus tree master branch (having your patch) and I am seeing 12% slowdown.
I am sure if I try more heavier benchmarks (such as stress-ng) then the slowdown will be even more.
Here are the detailed numbers:
Command: ./hackbench 32 Number of Tasks: 32*40 (== 1280) Average Time (without debug options): 3.10525 Average Time (with debug options): 3.471 (11.78% slower)
Command: ./hackbench 64 Number of Tasks: 64*40 (== 2560) Average Time (without debug options): 6.3015 Average Time (with debug options): 7.05875 (12.017% slower)
Command: ./hackbench 128 Number of Tasks: 128*40 (== 5120) Average Time (without debug options): 12.6275 Average Time (with debug options): 14.1455 (12.0214% slower)
It is this performance impact due to which other architectures (such as x86 and ARM64) don't have these debug options enabled in their defconfigs.
I will send a patch to move these debug options to separate debug defconfigs so that people have a way to build a debug kernel.
Regards, Anup
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