From: Florian Weimer <fweimer@redhat.com>
To: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Cc: libc-alpha@sourceware.org, Bruno Haible <bruno@clisp.org>
Subject: Re: [PATCH] time: Use CLOCK_REALTIME for time (BZ #30200)
Date: Tue, 07 Mar 2023 12:51:17 +0100 [thread overview]
Message-ID: <87bkl4pyoa.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <32a9fa9c-2714-9e18-a3e7-bcfc2d61cd87@linaro.org> (Adhemerval Zanella Netto's message of "Tue, 7 Mar 2023 08:45:05 -0300")
* Adhemerval Zanella Netto:
>> And of those original 17 ns, quite a bit is overhead from the
>> benchmarking loop. I guess applications could work around it by having
>> a background timer thread that increments a global variable and use that
>> instead of the time function call, but that seems not a great approach.
>
> Yes, this is expected since time call will be route through clock_gettime.
> Another fix would be to convince kernels developers to use CLOCK_REALTIME
> on vDSO as well.
No, that won't help. I think the crucial aspect for good x86-64
performance is that by using the time entry point, we tell the kernel
that it does not have to obtain microsecond or millisecond precision.
>> Based on previous feedback, I expect we'd have to carry a downstream
>> revert of this patch indefinitely, so I'm rather strongly against
>> applying it upstrean.
>
> To me it really seems like a over-optimization specially because 'time'
> has only second resolution.
I'm afraid that this will impact logging performance significantly in
some scenarios.
Thanks,
Florian
next prev parent reply other threads:[~2023-03-07 11:51 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 16:03 Adhemerval Zanella
2023-03-07 11:11 ` Florian Weimer
2023-03-07 11:45 ` Adhemerval Zanella Netto
2023-03-07 11:51 ` Florian Weimer [this message]
2023-03-07 11:57 ` Adhemerval Zanella Netto
2023-03-07 12:07 ` Florian Weimer
2023-03-08 5:51 ` Paul Eggert
2023-03-08 8:59 ` Florian Weimer
2023-03-08 23:08 ` Paul Eggert
2023-03-08 16:23 ` Bruno Haible
2023-03-08 16:57 ` Adhemerval Zanella Netto
2023-03-08 17:09 ` Florian Weimer
2023-03-08 17:46 ` Adhemerval Zanella Netto
2023-03-08 17:44 ` Bruno Haible
2023-03-08 17:50 ` Adhemerval Zanella Netto
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