On Thu, Apr 30, 2020 at 5:31 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, 30 Apr 2020 16:11:18 -0400 Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> wrote: > > > Sometimes the kernel doesn't take full advantage of system memory > > bandwidth, leading to a single CPU spending excessive time in > > initialization paths where the data scales with memory size. > > > > Multithreading naturally addresses this problem, and this series is the > > first step. > > > > It extends padata, a framework that handles many parallel singlethreaded > > jobs, to handle multithreaded jobs as well by adding support for > > splitting up the work evenly, specifying a minimum amount of work that's > > appropriate for one helper thread to do, load balancing between helpers, > > and coordinating them. More documentation in patches 4 and 7. > > > > The first user is deferred struct page init, a large bottleneck in > > kernel boot--actually the largest for us and likely others too. This > > path doesn't require concurrency limits, resource control, or priority > > adjustments like future users will (vfio, hugetlb fallocate, munmap) > > because it happens during boot when the system is otherwise idle and > > waiting on page init to finish. > > > > This has been tested on a variety of x86 systems and speeds up kernel > > boot by 6% to 49% by making deferred init 63% to 91% faster. > > How long is this up-to-91% in seconds? If it's 91% of a millisecond > then not impressed. If it's 91% of two weeks then better :) > > Relatedly, how important is boot time on these large machines anyway? > They presumably have lengthy uptimes so boot time is relatively > unimportant? Large machines indeed have a lengthy uptime, but they also can host a large number of VMs meaning that downtime of the host increases the downtime of VMs in cloud environments. Some VMs might be very sensible to downtime: game servers, traders, etc. > > IOW, can you please explain more fully why this patchset is valuable to > our users?
