From:   Thomas Gleixner <tglx@linutronix.de>
To:     Josh Stone <jistone@redhat.com>, Asahi Lina <lina@asahilina.net>,
        Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?utf-8?Q?Bj=C3=B6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
        John Stultz <jstultz@google.com>,
        Stephen Boyd <sboyd@kernel.org>
Cc:     linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org,
        asahi@lists.linux.dev
Subject: Re: [PATCH] rust: time: New module for timekeeping functions
In-Reply-To: <65ab5cb1-2dbe-e853-48ea-d1df87706cf0@redhat.com>
References: <20230221-gpu-up-time-v1-1-bf8fe74b7f55@asahilina.net>
 <87v8jvnqq4.ffs@tglx> <65ab5cb1-2dbe-e853-48ea-d1df87706cf0@redhat.com>
Date:   Tue, 21 Feb 2023 22:46:59 +0100
Message-ID: <87zg96n12k.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Tue, Feb 21 2023 at 09:13, Josh Stone wrote:

> On 2/21/23 4:32 AM, Thomas Gleixner wrote:
>> Now the problem is that 'Instant' in it's specification is bound to
>> CLOCK_MONOTONIC and there is no way to express CLOCK_BOOTTIME, but
>> that's a shortcoming of the spec which ignores CLOCK_BOOTTIME
>> completely. IOW, that's also a problem for user space.
>
> That's not exactly *specified* -- it's meant to be opaque time. It is
> documented that this currently uses clock_gettime monotonic on unix
> targets, but "Disclaimer: These system calls might change over time."
> CLOCK_MONOTONIC isn't even consistent across unix targets whether that
> counts suspended time. It's been debated if we should switch to
> CLOCK_BOOTTIME on Linux, but for now we're sticking to monotonic:

You'll need both when you want to implement substantial parts of the low
level user space stack in Rust. Same for CLOCK_TAI.

Thanks,

        tglx