From: Thomas Gleixner <tglx@linutronix.de>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: x86@kernel.org, Andy Lutomirski <luto@amacapital.net>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
Dexuan Cui <decui@microsoft.com>,
linux-kernel@vger.kernel.org, devel@linuxdriverproject.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method
Date: Thu, 9 Feb 2017 18:08:22 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.20.1702091806400.3604@nanos> (raw)
In-Reply-To: <20170209141052.18694-3-vkuznets@redhat.com>
On Thu, 9 Feb 2017, Vitaly Kuznetsov wrote:
> +#ifdef CONFIG_HYPERV_TSCPAGE
> +static notrace u64 vread_hvclock(int *mode)
> +{
> + const struct ms_hyperv_tsc_page *tsc_pg =
> + (const struct ms_hyperv_tsc_page *)&hvclock_page;
> + u64 sequence, scale, offset, current_tick, cur_tsc;
> +
> + while (1) {
> + sequence = READ_ONCE(tsc_pg->tsc_sequence);
> + if (!sequence)
> + break;
> +
> + scale = READ_ONCE(tsc_pg->tsc_scale);
> + offset = READ_ONCE(tsc_pg->tsc_offset);
> + rdtscll(cur_tsc);
> +
> + current_tick = mul_u64_u64_shr(cur_tsc, scale, 64) + offset;
> +
> + if (READ_ONCE(tsc_pg->tsc_sequence) == sequence)
> + return current_tick;
That sequence stuff lacks still a sensible explanation. It's fundamentally
different from the sequence counting we do in the kernel, so documentation
for it is really required.
Thanks,
tglx
next prev parent reply other threads:[~2017-02-09 17:08 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-09 14:10 [PATCH 0/2] x86/vdso: Add Hyper-V TSC page clocksource support Vitaly Kuznetsov
2017-02-09 14:10 ` [PATCH 1/2] hyperv: implement hv_get_tsc_page() Vitaly Kuznetsov
2017-02-09 18:24 ` Stephen Hemminger
2017-02-09 20:14 ` Thomas Gleixner
2017-02-09 23:17 ` Stephen Hemminger
2017-02-09 14:10 ` [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method Vitaly Kuznetsov
2017-02-09 17:08 ` Thomas Gleixner [this message]
2017-02-09 18:27 ` Stephen Hemminger
2017-02-10 12:25 ` Vitaly Kuznetsov
2017-02-10 12:28 ` Thomas Gleixner
2017-02-10 16:31 ` Stephen Hemminger
2017-02-10 18:01 ` Thomas Gleixner
2017-02-13 7:49 ` Dexuan Cui
2017-02-13 9:27 ` Thomas Gleixner
2017-02-13 19:06 ` Andy Lutomirski
2017-02-13 19:28 ` Thomas Gleixner
2017-02-09 20:45 ` KY Srinivasan
2017-02-09 22:55 ` Andy Lutomirski
2017-02-09 23:15 ` Stephen Hemminger
2017-02-10 12:15 ` Vitaly Kuznetsov
2017-02-10 11:06 ` Vitaly Kuznetsov
2017-02-10 11:15 ` Thomas Gleixner
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