linux-kernel - Re: __i915_spin

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Message-ID: <20151113153629.GB8939@kernel.dk>
Date:	Fri, 13 Nov 2015 08:36:29 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	Daniel Vetter <daniel.vetter@...ll.ch>,
	DRI Development <dri-devel@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: __i915_spin_request() sucks

Previous patch was obvious pre-coffee crap, this should work for using
ktime to spin max 1usec.

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 5cf4a1998273..21192e55c33c 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1148,17 +1148,18 @@ static bool missed_irq(struct drm_i915_private *dev_priv,
 
 static int __i915_spin_request(struct drm_i915_gem_request *req)
 {
-	unsigned long timeout;
+	ktime_t timeout;
 
 	if (i915_gem_request_get_ring(req)->irq_refcount)
 		return -EBUSY;
 
-	timeout = jiffies + 1;
+	timeout = ktime_get();
+	ktime_add_us(timeout, 1);
 	while (!need_resched()) {
 		if (i915_gem_request_completed(req, true))
 			return 0;
 
-		if (time_after_eq(jiffies, timeout))
+		if (ktime_after(ktime_get(), timeout))
 			break;
 
 		cpu_relax_lowlatency();

-- 
Jens Axboe

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