|
From: | Paolo Bonzini |
Subject: | Re: [Qemu-devel] [PATCH v4 18/29] hostmem: add file-based HostMemoryBackend |
Date: | Tue, 10 Jun 2014 13:43:27 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 |
Il 10/06/2014 13:35, Michael S. Tsirkin ha scritto:
Why? For example it would be useful for testing on machines that you don't have root for, and that do not have a hugetlbfs mount point. For example you could run the test case from the vhost-user's patches.Sounds useful, I guess we could allow this when running under qtest.Or TCG, or Xen. At this point, why single out KVM? (Also, "--enable-kvm -mem-path /dev/shm" works on 2.0, and it would be a regression in 2.1).It prints fprintf(stderr, "Warning: path not on HugeTLBFS: %s\n", path); Correct?
Yes.
I guess I agree then, hopefully the warning is enough. Maybe add an extra warning that performance will suffer.THP is not a magic wand and you can get slowness from memory fragmentation at any time.Right but there's a difference between "can get slowness when memory is overcommitted" and "will get slowness even on a mostly idle box".I would like to see the slowness on a real-world benchmark though. I suspect in most scenarios it would not matter.Weird. Things like kernel build time are known to be measureably improved by using THP.
Even measurable speedups in most scenarios would not matter. I don't care if a kernel compile takes 2 minutes vs. 110 seconds (for a 10% speedup), even though it's great that THP can speed up such a common task.
Paolo
[Prev in Thread] | Current Thread | [Next in Thread] |