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Date:      Tue, 10 Apr 2012 20:18:44 +0300
From:      Alexander Motin <mav@FreeBSD.org>
To:        Arnaud Lacombe <lacombar@gmail.com>
Cc:        freebsd-hackers@freebsd.org, Florian Smeets <flo@freebsd.org>, Jeff Roberson <jroberson@jroberson.net>, Andriy Gapon <avg@freebsd.org>, FreeBSD current <freebsd-current@freebsd.org>
Subject:   Re: [RFT][patch] Scheduling for HTT and not only
Message-ID:  <4F846B74.9080504@FreeBSD.org>
In-Reply-To: <CACqU3MXo__hiKf%2Bs31c5WFZmVO_T8mJgu4A=KkMF=MWp8VoW4w@mail.gmail.com>
References:  <4F2F7B7F.40508@FreeBSD.org> <4F366E8F.9060207@FreeBSD.org> <4F367965.6000602@FreeBSD.org> <4F396B24.5090602@FreeBSD.org> <alpine.BSF.2.00.1202131012270.2020@desktop> <4F3978BC.6090608@FreeBSD.org> <alpine.BSF.2.00.1202131108460.2020@desktop> <4F3990EA.1080002@FreeBSD.org> <4F3C0BB9.6050101@FreeBSD.org> <alpine.BSF.2.00.1202150949480.2020@desktop> <4F3E807A.60103@FreeBSD.org> <CACqU3MWEC4YYguPQF_d%2B_i_CwTc=86hG%2BPbxFgJQiUS-=AHiRw@mail.gmail.com> <4F3E8858.4000001@FreeBSD.org> <CACqU3MWZj503xN_-wr6s%2BXOB7JGhhBgaWW0gOX60KJvU3Y=Rig@mail.gmail.com> <4F7DE863.6080607@FreeBSD.org> <4F833F3D.7070106@FreeBSD.org> <CACqU3MXo__hiKf%2Bs31c5WFZmVO_T8mJgu4A=KkMF=MWp8VoW4w@mail.gmail.com>

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On 04/10/12 19:58, Arnaud Lacombe wrote:
> 2012/4/9 Alexander Motin<mav@freebsd.org>:
>> [...]
>>
>> I have strong feeling that while this test may be interesting for profiling,
>> it's own results in first place depend not from how fast scheduler is, but
>> from the pipes capacity and other alike things. Can somebody hint me what
>> except pipe capacity and context switch to unblocked receiver prevents
>> sender from sending all data in batch and then receiver from receiving them
>> all in batch? If different OSes have different policies there, I think
>> results could be incomparable.
>>
> Let me disagree on your conclusion. If OS A does a task in X seconds,
> and OS B does the same task in Y seconds, if Y>  X, then OS B is just
> not performing good enough. Internal implementation's difference for
> the task can not be waived as an excuse for result's comparability.

Sure, numbers are always numbers, but the question is what are they 
showing? Understanding of the test results is even more important for 
purely synthetic tests like this. Especially when one test run gives 25 
seconds, while another gives 50. This test is not completely clear to me 
and that is what I've told.

-- 
Alexander Motin



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