linux-kernel - [PATCH 06/10] powerpc/vas: Reduce polling interval for busy state

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Message-Id: <1505621128-23877-7-git-send-email-sukadev@linux.vnet.ibm.com>
Date:   Sat, 16 Sep 2017 21:05:24 -0700
From:   Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        mikey@...ling.org, hbabu@...ibm.com, linuxppc-dev@...abs.org,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH 06/10] powerpc/vas: Reduce polling interval for busy state

A VAS window is normally in "busy" state for only a short duration.
Reduce the time we wait for the window to go to "not-busy" state to
speed-up vas_win_close() a bit.

Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
---
 arch/powerpc/platforms/powernv/vas-window.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/vas-window.c b/arch/powerpc/platforms/powernv/vas-window.c
index 95622a9..1422cdd 100644
--- a/arch/powerpc/platforms/powernv/vas-window.c
+++ b/arch/powerpc/platforms/powernv/vas-window.c
@@ -1060,21 +1060,23 @@ int vas_paste_crb(struct vas_window *txwin, int offset, bool re)
 }
 EXPORT_SYMBOL_GPL(vas_paste_crb);
 
+/*
+ * Wait for the window to go to "not-busy" state. It should only take a
+ * short time to queue a CRB, so window should not be busy for too long.
+ * Trying 5ms intervals.
+ */
 static void poll_window_busy_state(struct vas_window *window)
 {
 	int busy;
 	u64 val;
 
 retry:
-	/*
-	 * Poll Window Busy flag
-	 */
 	val = read_hvwc_reg(window, VREG(WIN_STATUS));
 	busy = GET_FIELD(VAS_WIN_BUSY, val);
 	if (busy) {
 		val = 0;
 		set_current_state(TASK_UNINTERRUPTIBLE);
-		schedule_timeout(HZ);
+		schedule_timeout(msecs_to_jiffies(5));
 		goto retry;
 	}
 }
-- 
2.7.4