On Thu 04-10-18 15:42:52, Bart Van Assche wrote: > On Thu, 2018-10-04 at 22:39 +0200, Paolo Valente wrote: > > No, kernel build is, for evident reasons, one of the workloads I cared > > most about. Actually, I tried to focus on all my main > > kernel-development tasks, such as also git checkout, git merge, git > > grep, ... > > > > According to my test results, with BFQ these tasks are at least as > > fast as, or, in most system configurations, much faster than with the > > other schedulers. Of course, at the same time the system also remains > > responsive with BFQ. > > > > You can repeat these tests using one of my first scripts in the S > > suite: kern_dev_tasks_vs_rw.sh (usually, the older the tests, the more > > hypertrophied the names I gave :) ). > > > > I stopped sharing also my kernel-build results years ago, because I > > went on obtaining the same, identical good results for years, and I'm > > aware that I tend to show and say too much stuff. > > On my test setup building the kernel is slightly slower when using the BFQ > scheduler compared to using scheduler "none" (kernel 4.18.12, NVMe SSD, > single CPU with 6 cores, hyperthreading disabled). I am aware that the > proposal at the start of this thread was to make BFQ the default for devices > with a single hardware queue and not for devices like NVMe SSDs that support > multiple hardware queues. > > What I think is missing is measurement results for BFQ on a system with > multiple CPU sockets and against a fast storage medium. Eliminating > the host lock from the SCSI core yielded a significant performance > improvement for such storage devices. Since the BFQ scheduler locks and > unlocks bfqd->lock for every dispatch operation it is very likely that BFQ > will slow down I/O for fast storage devices, even if their driver only > creates a single hardware queue. Well, I'm not sure why that is missing. I don't think anyone proposed to default to BFQ for such setup? Neither was anyone claiming that BFQ is better in such situation... The proposal has been: Default to BFQ for slow storage, leave it to deadline-mq otherwise. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
