From: Denys Vlasenko <dvlasenk@redhat.com>
To: "Christian König" <christian.koenig@amd.com>,
"Ingo Molnar" <mingo@kernel.org>,
"Andy Lutomirski" <luto@kernel.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Alex Deucher" <alexander.deucher@amd.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
"Vinod Koul" <vinod.koul@intel.com>,
"Johannes Berg" <johannes.berg@intel.com>,
"Sara Sharon" <sara.sharon@intel.com>,
"Adrian Hunter" <adrian.hunter@intel.com>,
"Linus Torvalds" <torvalds@linux-foundation.org>
Cc: x86@kernel.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: RFC: Petition Intel/AMD to add POPF_IF insn
Date: Wed, 17 Aug 2016 20:34:50 +0200 [thread overview]
Message-ID: <1a3e565b-1f27-dbd5-5111-ed87a1dc2aa0@redhat.com> (raw)
In-Reply-To: <64bd8281-aeb4-391b-90c6-3f5e44f0ce07@amd.com>
On 08/17/2016 07:30 PM, Christian König wrote:
>> But in my measurements POPF is not fast even in the case where restored
>> flags are not changed at all:
>>
>> mov $200*1000*1000, %eax
>> pushf
>> pop %rbx
>> .balign 64
>> loop: push %rbx
>> popf
>> dec %eax
>> jnz loop
>>
>> # perf stat -r20 ./popf_1g
>> 4,929,012,093 cycles # 3.412 GHz ( +- 0.02% )
>> 835,721,371 instructions # 0.17 insn per cycle ( +- 0.02% )
>> 1.446185359 seconds time elapsed ( +- 0.46% )
>>
>> If I replace POPF with a pop into an unused register, I get this:
>
> You are comparing apples and bananas here.
Yes, I know. Pop into a register here is basically free.
I'd also add a STI and measure how much it takes to
enable interrupts, but unfortunately STI throws a #GP
in CPL 3.
next prev parent reply other threads:[~2016-08-17 18:35 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-17 17:20 Denys Vlasenko
2016-08-17 17:30 ` Christian König
2016-08-17 18:34 ` Denys Vlasenko [this message]
2016-08-17 17:32 ` Linus Torvalds
2016-08-17 18:41 ` Denys Vlasenko
[not found] ` <CA+55aFwmxwQBkyDjombS4cy1q=a_buhmDjDnaa8rdC8ZDaDYEA@mail.gmail.com>
2016-08-17 19:13 ` Andy Lutomirski
2016-08-17 19:26 ` Denys Vlasenko
2016-08-17 19:32 ` Linus Torvalds
2016-08-17 19:35 ` Denys Vlasenko
2016-08-17 19:54 ` Linus Torvalds
2016-08-17 19:37 ` Linus Torvalds
2016-08-17 21:26 ` Linus Torvalds
2016-08-17 21:35 ` Linus Torvalds
2016-08-17 21:43 ` Andy Lutomirski
2016-08-17 21:48 ` Linus Torvalds
2016-08-18 13:26 ` Denys Vlasenko
2016-08-18 17:24 ` Linus Torvalds
2016-08-18 17:47 ` Denys Vlasenko
2016-08-18 17:49 ` Denys Vlasenko
2016-08-19 10:54 ` Paolo Bonzini
2016-08-31 11:12 ` Denys Vlasenko
2016-08-18 9:21 ` Denys Vlasenko
2016-08-18 12:18 ` Denys Vlasenko
2016-08-18 17:22 ` Paolo Bonzini
2016-08-17 19:29 ` Linus Torvalds
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