Log in

No account? Create an account

Previous Entry

I build quite a few Linux kernels, mostly in support of my deep and abiding rcutorture habit. These builds can take some time, even on modern laptops, but they are nevertheless amazingly fast compared to the build times of the much smaller projects I worked on in decades past. Additionally, build times are way down in the noise when I am doing multi-hour rcutorture runs. So much so that I don't bother with cut-down kernel configurations, especially given that cut-down configurations are an excellent way to fail to spot subtle RCU API problems.

Still, faster builds do have their advantages, especially when doing a series of short tests, such as when chasing down that rarest of creatures, an RCU bug that reproduces reliably within a few minutes of boot. Which is exactly what I was doing yesterday. And during that time, a five-minute kernel build time was much more annoying than it normally would be.

But that is why we have ccache, a tool that is considerably more attractive than it was back when my laptop's mass storage weighed in at “only” a few tens of gigabytes. With a bit of help from here, here, and the ccache man page, I got ccache up and running, and somewhat later got it actually making kernel builds go faster. Sometimes considerably more than an order of magnitude faster!

But I do get spoiled really quickly.

You see, the first ccache build goes no faster than a normal build because the cache is initially empty. And yes, a five, six, or even seven-minute build was just fine a couple of days ago: After all, there is always some small task that needs to be done. But having just witnessed builds completing in way less than one minute, even a five-minute wait now seemed horribly slow. And a five-minute build is what I get the first time I run a given rcutorture scenario. Or after I modify an rcutorture scenario. Or if I specify unusual arguments to rcutorture's --kconfig command-line option. Or if I modify a heavily used include file. Or when I configured ccache's cache size too small.

Nevertheless, I most definitely should have installed ccache a very long time ago! :-)