[PATCH] Revert "xen/cpufreq: fix usages of align_timer() in the on-demand governor"

[Jason Andryuk <jason.andryuk@xxxxxxx>]

The original commit showed a ~6% regression in a benchmark.  The call to
align_timer(firsttick, period) rounds firsttick up to the next mutiple
of the period, if firsttick % period != 0:

align_timer(0, period)          -> 0
align_timer(1, period)          -> period
align_timer(period, period)     -> period
align_timer(period + 1, period) -> 2 * period

So adding the period (sampling_rate) before calling align_timer() will
in most cases incease the expiration to 2 * period (sampling_rate) (the
exception being firsttick % period == 0).  This longer timer slows the
reaction time of the algorithm.

This reverts commit a0ed5bcfbeee81c91c574ad484faa057054eaf09.

Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
---
This is backported in stable trees and should be reverted there as well
(found in 4.20.3).

A Fixes seems superfluous and not normally used with a revert, but if
needed:
Fixes: a0ed5bcfbeee ("xen/cpufreq: fix usages of align_timer() in the on-demand 
governor")
---
 xen/drivers/cpufreq/cpufreq_ondemand.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/xen/drivers/cpufreq/cpufreq_ondemand.c 
b/xen/drivers/cpufreq/cpufreq_ondemand.c
index 0d94c0e464..537695eaab 100644
--- a/xen/drivers/cpufreq/cpufreq_ondemand.c
+++ b/xen/drivers/cpufreq/cpufreq_ondemand.c
@@ -185,8 +185,7 @@ static void cf_check do_dbs_timer(void *dbs)
     dbs_check_cpu(dbs_info);
 
     set_timer(&per_cpu(dbs_timer, dbs_info->cpu),
-              align_timer(NOW() + dbs_tuners_ins.sampling_rate,
-                          dbs_tuners_ins.sampling_rate));
+            align_timer(NOW() , dbs_tuners_ins.sampling_rate));
 }
 
 static void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
@@ -401,6 +400,6 @@ void cpufreq_dbs_timer_resume(void)
             (void)cmpxchg(stoppable, -1, 1);
         }
         else
-            set_timer(t, align_timer(t->expires, 
dbs_tuners_ins.sampling_rate));
+            set_timer(t, align_timer(now, dbs_tuners_ins.sampling_rate));
     }
 }
-- 
2.54.0