From: Thomas Gleixner <tglx@linutronix.de>
To: 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>
Cc: Steven Noonan <steven@uplinklabs.net>,
usama.anjum@collabora.com, kernel@collabora.com
Subject: Re: [PATCH 3/3] x86/tsc: don't check for random warps if using direct sync
Date: Wed, 24 Aug 2022 16:14:49 +0200 [thread overview]
Message-ID: <87sfllybhi.ffs@tglx> (raw)
In-Reply-To: <20220808113954.345579-3-usama.anjum@collabora.com>
On Mon, Aug 08 2022 at 16:39, Muhammad Usama Anjum wrote:
> There's some overhead in writing and reading MSR_IA32_TSC. We try to
> account for it. But sometimes overhead gets under or over estimated.
> When we retry syncing, it sees the clock "go backwards". Hence,
> ignore random wrap if using direct sync.
This is just wrong. If the sync test can observe clock going backwards
then it can be observed during runtime too. Preventing that is the whole
point of the TSC sync exercise.
Thanks,
tglx
next prev parent reply other threads:[~2022-08-24 14:14 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-08 11:39 [PATCH 1/3] x86/tsc: implement tsc=directsync for systems without IA32_TSC_ADJUST Muhammad Usama Anjum
2022-08-08 11:39 ` [PATCH 2/3] x86: touch clocksource watchdog after syncing TSCs Muhammad Usama Anjum
2022-08-08 11:39 ` [PATCH 3/3] x86/tsc: don't check for random warps if using direct sync Muhammad Usama Anjum
2022-08-24 14:14 ` Thomas Gleixner [this message]
2022-08-23 16:50 ` [PATCH 1/3] x86/tsc: implement tsc=directsync for systems without IA32_TSC_ADJUST Muhammad Usama Anjum
2022-08-24 14:13 ` Thomas Gleixner
2022-08-25 7:21 ` Muhammad Usama Anjum
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