Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 1 Jul 2015 10:33:54 -0700 | Subject | Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr |
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On Wed, Jul 1, 2015 at 9:38 AM, Brown, Len <len.brown@intel.com> wrote: > BTW. I've had a discussion w/ LLNL about their needs, > both for security and performance. For security, as concluded > by this thread, a white list is the only way to go. > I'm thinking a bit-vector of allowed MSR offsets... > For performance, they absolutely can not afford a system call > for every single MSR access.
I'm surprised. On a sane kernel, a syscall is about 120 cycles. Just rdmsr to an unoptimized MSR is probably fifty cycles, I'd guess.
Of course, LLNL is probably using NOHZ_FULL, which is currently very, very slow. Work is afoot to fix that.
> Here an ioctl to have the > msr driver perform a vector of accesses in a single system > call seems the way to go. I can prototype both of these > using turbostat as the customer.
How about preadv?
--Andy
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