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Commit 955a23eb authored by Eric Anholt's avatar Eric Anholt Committed by Dave Airlie
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drm: Use a little stash on the stack to avoid kmalloc in most DRM ioctls. 



The kmalloc was taking up about 1.5% of the CPU on an ioctl-heavy workload
(x11perf -aa10text on 965).  Initial results look like they have a
corresponding improvement in performance for aa10text, but more numbers might
not hurt.

Thanks to ajax for pointing out this performance regression I'd introduced
back in 2007.

[airlied: well I introduced it sneakily inside Eric's patch]

Signed-off-by: default avatarEric Anholt <eric@anholt.net>
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent af7ae351

drivers/gpu/drm/drm_drv.c

+10 −5
Original line number Diff line number Diff line
@@ -421,6 +421,7 @@ int drm_ioctl(struct inode *inode, struct file *filp, 
	drm_ioctl_t *func;

	unsigned int nr = DRM_IOCTL_NR(cmd);

	int retcode = -EINVAL;

	char stack_kdata[128];

	char *kdata = NULL;



	atomic_inc(&dev->ioctl_count);
@@ -459,12 +460,16 @@ int drm_ioctl(struct inode *inode, struct file *filp, 
		retcode = -EACCES;

	} else {

		if (cmd & (IOC_IN | IOC_OUT)) {

			if (_IOC_SIZE(cmd) <= sizeof(stack_kdata)) {

				kdata = stack_kdata;

			} else {

				kdata = kmalloc(_IOC_SIZE(cmd), GFP_KERNEL);

				if (!kdata) {

					retcode = -ENOMEM;

					goto err_i1;

				}

			}

		}



		if (cmd & IOC_IN) {

			if (copy_from_user(kdata, (void __user *)arg,
@@ -483,7 +488,7 @@ int drm_ioctl(struct inode *inode, struct file *filp, 
	}



      err_i1:

	if (kdata)

	if (kdata != stack_kdata)

		kfree(kdata);

	atomic_dec(&dev->ioctl_count);

	if (retcode)