4 ms·
The main thing affecting performance at the userspace/kernel boundary these days is Spectre and Meltdown mitigations, FWIW...
by zozbot123 8y ago
The main thing affecting performance at the userspace/kernel boundary these days is Spectre and Meltdown mitigations, FWIW...
- mpweiher 8y agoYeah, when I ran the same tests a little later and with the Spectre/Meltdown patches (+APFS, which also didn't help), the mkfile I/O rate had a further precipitous drop to ~80MB/s.
- vlovich123 8y agoNo, userspace/kernel transitions are always and will always be slow. Every time it happens you've got to do a context switch which is super-expensive + cache unfriendly. You also pay a penalty keeping the kernel mapped at all times in terms of more pressure on the TLB but due to Spectre and Meltdown mitigations the kernel has actually been unmapped hurting the performance of switching into kernel further although this will be undone eventually.