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Index > Main > Great read about Haswell CPU Microarchitecture

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Joined: 04 Mar 2008
Posts: 563
Location: Germany
randall wrote:
..as expected...Speed improvement in current (not compiled for a new architecture) programs is from 5% to 20%.

ok, as expected, you say, on normal app; i read docs again, and the only parameter bound to this expectation seems to be
the ROB expansion to 192 entry, +15% above Sandy bridge.

supposing tests are correct there, we should admit the existance of something wrong in the uop cache, i.e in its design or
in programming it from those test software.

it should be 2 loads + 1 store and 5 instructions per cycle !
or the +2 ports come to be practically unused

de facto while using vectors and FMA (where there's practically no i-caches misses) all seems running fine, as announced by Intel.
Very Happy

Post 09 Jun 2013, 12:04
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Joined: 12 Apr 2012
Posts: 125
tthsqe wrote:
Does anybody know if vdivpd/vsqrtpd is still split internally (thus doubling the latency of divpd/sqrtpd) on haswell? I noticed this when there was not a 2:1 performance ratio on AVX:SSE code for the mandelbox on sandy/ivebridge. Unfortuately, the mandelbox uses a divide, and this ratio is only 1.3:1. Sad

I have asked in clax newsgroup and got this list:

Seems that situation is same as for previous generations.
Post 11 Jun 2013, 20:23
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Joined: 20 May 2009
Posts: 739
thanks for the info. I was previously doing a divide BEFORE clamping to [0.25,1]. I did see some decent improvement by dividing AFTER clamping to [0.25,1], as the divpd instruction is faster on powers of 2. This improvement is good enough that the rcps+newton solution is not better.
Post 11 Jun 2013, 20:32
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