On Thu, Jul 16, 2020 at 3:14 AM Srinivas Pandruvada
[off-list ref] wrote:

On Wed, 2020-07-15 at 14:35 -0700, Francisco Jerez wrote:

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"Rafael J. Wysocki" [off-list ref] writes:

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On Wed, Jul 15, 2020 at 2:09 AM Francisco Jerez <
currojerez@riseup.net> wrote:

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"Rafael J. Wysocki" [off-list ref] writes:

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From: Rafael J. Wysocki <redacted>

[...]

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I don't think that's accurate.  I've looked at hundreds of
traces

while
my series [1] was in control of HWP_REQ_MAX and I've never seen an
excursion above the maximum HWP_REQ_MAX control specified by it
within a
given P-state domain, even while that maximum specified was well into
the turbo range.  So, yeah, I agree that HWP_REQ_MAX is nothing like
a
hard limit, particularly when multiple threads are running on the
same
clock domain, but the processor will still make its best effort to
limit
the clock frequency to the maximum of the requested maximums, even if
it
happens to be within the turbo range.  That doesn't make it useless.
The exact same thing can be said about controlling HWP_REQ_MIN as
you're
doing now in this revision of your patch, BTW.

If you don't believe me here is the turbostat sample with maximum
Bzy_MHz I get on the computer I'm sitting on right now while
compiling a
kernel on CPU0 if I set HWP_REQ_MAX to 0x1c (within the turbo range):

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Core    CPU     Avg_MHz
Busy%   Bzy_MHz            HWP_REQ      PkgWatt CorWatt
-       -       757     27.03   2800    0x0000000000000000      7.1
3    4.90
0       0       2794    99.77   2800    0x0000000080001c04      7.1
3    4.90
0       2       83      2.98    2800    0x0000000080001c04
1       1       73      2.60    2800    0x0000000080001c04
1       3       78      2.79    2800    0x0000000080001c04

With the default HWP_REQUEST:

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Core    CPU     Avg_MHz
Busy%   Bzy_MHz            HWP_REQ      PkgWatt CorWatt
-       -       814     27.00   3015    0x0000000000000000      8.4
9    6.18
0       0       2968    98.24   3021    0x0000000080001f04      8.4
9    6.18
0       2       84      2.81    2982    0x0000000080001f04
1       1       99      3.34    2961    0x0000000080001f04
1       3       105     3.60    2921    0x0000000080001f04

Correct. In HWP mode this is possible to lower limit in turbo region
conditionally. In legacy mode you can't with turbo activation ratio.

But what we don't want set max and min perf and use like desired to run
at a P-state overriding HWP or limit the range where HWP can't do any
meaningful selection.

That's a good point too IMO.