linux-kernel - [PATCH 1/7] tools/power turbostat: bugfix: GFXMHz column not changing

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Date:   Wed, 12 Apr 2017 20:08:47 -0400
From:   Len Brown <lenb@...nel.org>
To:     rjw@...ysocki.net, linux-pm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Len Brown <len.brown@...el.com>
Subject: [PATCH 1/7] tools/power turbostat: bugfix: GFXMHz column not changing

From: Len Brown <len.brown@...el.com>

turbostat displays a GFXMHz column, which comes from reading
/sys/class/graphics/fb0/device/drm/card0/gt_cur_freq_mhz

But GFXMHz was not changing, even when a manual
cat /sys/class/graphics/fb0/device/drm/card0/gt_cur_freq_mhz
showed a new value.

It turns out that a rewind() on the open file is not sufficient,
fflush() (or a close/open) is needed to read fresh values.

Reported-by: Yaroslav Isakov <yaroslav.isakov@...il.com>
Signed-off-by: Len Brown <len.brown@...el.com>
---
 tools/power/x86/turbostat/turbostat.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
index 828dccd3f01e..d7fb6bcb2744 100644
--- a/tools/power/x86/turbostat/turbostat.c
+++ b/tools/power/x86/turbostat/turbostat.c
@@ -2485,8 +2485,10 @@ int snapshot_gfx_mhz(void)
 
 	if (fp == NULL)
 		fp = fopen_or_die("/sys/class/graphics/fb0/device/drm/card0/gt_cur_freq_mhz", "r");
-	else
+	else {
 		rewind(fp);
+		fflush(fp);
+	}
 
 	retval = fscanf(fp, "%d", &gfx_cur_mhz);
 	if (retval != 1)
-- 
2.11.0.161.g6610af872