From: Peter Zijlstra <peterz@infradead.org>
To: Steven Noonan <steven@uplinklabs.net>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Muhammad Usama Anjum <usama.anjum@collabora.com>,
Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>,
"Guilherme G. Piccoli" <gpiccoli@igalia.com>,
kernel@collabora.com
Subject: Re: Direct rdtsc call side-effect
Date: Fri, 2 Jun 2023 08:45:15 +0200 [thread overview]
Message-ID: <20230602064515.GA620383@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <YveIgyZYN48CEPKlxf6r_CfVBGuON83brWVxnVJGtXW70bDprPOiAtEMeKELDJj3lVYuZm7fTDQnMIuheMN01YfqfWbCGYia0uWcWIx59oM=@uplinklabs.net>
On Thu, Jun 01, 2023 at 09:41:15PM +0000, Steven Noonan wrote:
> On Thursday, June 1st, 2023 at 1:31 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> > What about kernel based emulation? You could tie it into user_dispatch
> > and have a user_dispatch tsc offset.
> >
>
> > So regular kernel emulation simply returns the native value (keeps the
> > VDSO working for one), but then from a user_dispatch range, it returns
> > +offset.
> >
>
> > That is; how slow is the below?
>
> It's around 1800-1900 clock cycles on this system
Much more expensive than the actual instruction ofcourse, but that seems
eminently usable.
> (modified patch attached, compile fix + rdtscp support).
Right, that's what I get for writing 'patches' while falling asleep :/
> Since faulting would still make the vDSO clocks go through this path
> we'd have to be careful that whatever offsets we throw into this path
> don't affect the correctness of the other clocks.
Hence the suggested tie-in with user-dispatch; only add the offset when
the IP is from the user-dispatch range.
next prev parent reply other threads:[~2023-06-02 6:45 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-01 8:45 Direct rdtsc call side-effect Muhammad Usama Anjum
2023-06-01 8:56 ` Peter Zijlstra
2023-06-01 8:58 ` Peter Zijlstra
2023-06-01 10:31 ` Thomas Gleixner
2023-06-01 10:26 ` Thomas Gleixner
2023-06-01 18:20 ` Thomas Gleixner
2023-06-01 19:07 ` Steven Noonan
2023-06-01 19:31 ` H. Peter Anvin
2023-06-01 20:10 ` Thomas Gleixner
2023-06-01 20:13 ` Thomas Gleixner
2023-06-01 20:31 ` Peter Zijlstra
2023-06-01 21:41 ` Steven Noonan
2023-06-02 6:45 ` Peter Zijlstra [this message]
2023-06-05 10:27 ` David Laight
2023-06-05 14:43 ` Thomas Gleixner
2023-06-05 15:54 ` David Laight
2023-06-05 16:32 ` H. Peter Anvin
2023-06-06 8:23 ` David Laight
2023-06-09 0:14 ` H. Peter Anvin
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