linux-kernel - [PATCH 4.9 096/104] tools/power turbostat: bugfix: GFXMHz column not changing

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Date:   Fri,  6 Oct 2017 10:52:14 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Yaroslav Isakov <yaroslav.isakov@...il.com>,
        Len Brown <len.brown@...el.com>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.9 096/104] tools/power turbostat: bugfix: GFXMHz column not changing

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

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


[ Upstream commit 22048c5485503749754b3b5daf9d99ef89fcacdc ]

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>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 tools/power/x86/turbostat/turbostat.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/tools/power/x86/turbostat/turbostat.c
+++ b/tools/power/x86/turbostat/turbostat.c
@@ -2003,8 +2003,10 @@ 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)