On 1/17/20 12:29 PM, Waiman Long wrote: > On 1/17/20 12:05 PM, Linus Torvalds wrote: >> [ on mobile, sorry for html crud ] >> >> On Fri, Jan 17, 2020, 08:53 Waiman Long <longman@xxxxxxxxxx >> <mailto:longman@xxxxxxxxxx>> wrote: >> >> >> I had found that parallel kernel build became much slower when a >> 5.5-based kernel is used. On a 2-socket 96-thread x86-64 system, the >> "make -j88" time increased from less than 3 minutes with the 5.4 >> kernel >> to more than double with the 5.5 kernel. >> >> >> I suspect you may have hit the same bug in the GNU make jobserver >> that I did. >> >> It's timing-sensitive, and under the right circumstances the make >> jobserver loses job tickets to other jobservers that have a child >> that died, but they are blocked waiting for a new ticket, so they >> aren't releasing (or re-using) the one that the child death would >> free up. >> >> End result: a big lack of parallelism, and a much slower build. >> >> GNU make v4.2.1 is buggy. The fix was done over two years ago, but >> there hasn't been a new release since then, so a lot of distributions >> have the buggy version.. >> >> The fix is commit b552b05 ("[SV 51159] Use a non-blocking read with >> pselect to avoid hangs.") In the make the git tree. >> >> >> Linus > > Thanks for the information. > > Yes, I did use make v4.2.1 which is the version that is shipped in > RHEL8. I will build new make and try it. > > Thanks, > Longman > I built a make with the lastest make git tree and the problem was gone with the new make. So it was a bug in make not the kernel. Sorry for the noise. Cheers, Longman
