linux-kernel - cpu-freq: running the perf increases the data rate?

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Message-ID: <CAPY=qRRekJonX_iX3s4bfietm9D_GM+S4cDGXbj9nMOefJBdTw@mail.gmail.com>
Date:   Thu, 27 Aug 2020 22:25:16 +0530
From:   Subhashini Rao Beerisetty <subhashbeerisetty@...il.com>
To:     linux-pm@...r.kernel.org,
        kernelnewbies <kernelnewbies@...nelnewbies.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: cpu-freq: running the perf increases the data rate?

 [ Please keep me in CC as I'm not subscribed to the list]

Hi all,

I have an application which finds the data rate over the PCIe
interface. I’m getting the lesser data rate in one of my Linux X86
systems.
When I change the scaling_governor from "powersave" to "performance"
mode for each CPU, then there is slight improvement in the PCIe data
rate.
Parallely I started profiling the workload with perf. Whenever I start
running the profile command “perf stat -a -d -p <PID>” surprisingly
the application resulted in excellent data rate over PCIe, but when I
kill the perf command again PCIe data rate drops. I am really confused
about this behavior.Any clues from this behaviour?

Also I noticed my system not having the 'cpuinfo_cur_freq' sys file.
Is that okay?
cat: /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq: No such
file or directory

-- 
Thanks,