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Date:      Tue, 15 Jul 2014 10:43:48 -0500
From:      Alan Cox <alc@rice.edu>
To:        John Baldwin <jhb@freebsd.org>, Konstantin Belousov <kostikbel@gmail.com>
Cc:        svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Nathan Whitehorn <nwhitehorn@freebsd.org>
Subject:   Re: svn commit: r268624 - head/sys/dev/vt/hw/efifb
Message-ID:  <53C54C34.4090408@rice.edu>
In-Reply-To: <201407151001.38146.jhb@freebsd.org>
References:  <201407141742.s6EHgMNt094168@svn.freebsd.org> <20140714175345.GK93733@kib.kiev.ua> <201407151001.38146.jhb@freebsd.org>
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On 07/15/2014 09:01, John Baldwin wrote:
> On Monday, July 14, 2014 1:53:45 pm Konstantin Belousov wrote:
>> On Mon, Jul 14, 2014 at 05:42:22PM +0000, Nathan Whitehorn wrote:
>>> Author: nwhitehorn
>>> Date: Mon Jul 14 17:42:22 2014
>>> New Revision: 268624
>>> URL: http://svnweb.freebsd.org/changeset/base/268624
>>>
>>> Log:
>>>   On my Lenovo laptop, the firmware maps the EFI framebuffer with MTRRs 
> set
>>>   to uncacheable. This leads to execrable console performance. Once PMAP 
> is
>>>   up, remap the framebuffer as write-combining. This reduces boot time on 
> my
>>>   laptop by 60% when booting with EFI.
>>>   
>>>   MFC after:	2 weeks
>>>
>>> Modified:
>>>   head/sys/dev/vt/hw/efifb/efifb.c
>>>
>>> Modified: head/sys/dev/vt/hw/efifb/efifb.c
>>>
> ==============================================================================
>>> --- head/sys/dev/vt/hw/efifb/efifb.c	Mon Jul 14 17:16:09 2014	
> (r268623)
>>> +++ head/sys/dev/vt/hw/efifb/efifb.c	Mon Jul 14 17:42:22 2014	
> (r268624)
>>> @@ -53,6 +53,7 @@ __FBSDID("$FreeBSD$");
>>>  
>>>  static vd_init_t vt_efifb_init;
>>>  static vd_probe_t vt_efifb_probe;
>>> +static void vt_efifb_remap(void *efifb_data);
>>>  
>>>  static struct vt_driver vt_efifb_driver = {
>>>  	.vd_name = "efifb",
>>> @@ -68,6 +69,8 @@ static struct vt_driver vt_efifb_driver 
>>>  static struct fb_info local_info;
>>>  VT_DRIVER_DECLARE(vt_efifb, vt_efifb_driver);
>>>  
>>> +SYSINIT(efifb_remap, SI_SUB_KMEM, SI_ORDER_ANY, vt_efifb_remap, 
> &local_info);
>>> +
>>>  static int
>>>  vt_efifb_probe(struct vt_device *vd)
>>>  {
>>> @@ -133,9 +136,9 @@ vt_efifb_init(struct vt_device *vd)
>>>  	info->fb_size = info->fb_height * info->fb_stride;
>>>  	info->fb_pbase = efifb->fb_addr;
>>>  	/*
>>> -	 * We could use pmap_mapdev here except that the kernel pmap
>>> -	 * hasn't been created yet and hence any attempt to lock it will
>>> -	 * fail.
>>> +	 * Use the direct map as a crutch until pmap is available. Once pmap
>>> +	 * is online, the framebuffer will be remapped by vt_efifb_remap()
>>> +	 * using pmap_mapdev_attr().
>>>  	 */
>>>  	info->fb_vbase = PHYS_TO_DMAP(efifb->fb_addr);
>>>  
>>> @@ -163,3 +166,22 @@ vt_efifb_init(struct vt_device *vd)
>>>  
>>>  	return (CN_INTERNAL);
>>>  }
>>> +
>>> +static void
>>> +vt_efifb_remap(void *xinfo)
>>> +{
>>> +	struct fb_info *info = xinfo;
>>> +
>>> +	if (info->fb_pbase == 0)
>>> +		return;
>>> +
>>> +	/*
>>> +	 * Remap as write-combining. This massively improves performance and
>>> +	 * happens very early in kernel initialization, when everything is
>>> +	 * still single-threaded and interrupts are off, so replacing the
>>> +	 * mapping address is safe.
>>> +	 */
>>> +	info->fb_vbase = (intptr_t)pmap_mapdev_attr(info->fb_pbase,
>>> +	    info->fb_size, VM_MEMATTR_WRITE_COMBINING);
>>> +}
>>> +
>> Could you use pmap_change_attr() ? This would save some KVA.
> I think that is a no-op in this case.  pmap_mapdev_attr() on amd64 is already 
> going to re-use the existing DMAP mapping after doing pmap_change_attr() on 
> it.
>

Yes, it automatically uses the direct map:

void *
pmap_mapdev_attr(vm_paddr_t pa, vm_size_t size, int mode)
{
        vm_offset_t va, offset;
        vm_size_t tmpsize;

        /*
         * If the specified range of physical addresses fits within the
direct
         * map window, use the direct map.
         */
        if (pa < dmaplimit && pa + size < dmaplimit) {
                va = PHYS_TO_DMAP(pa);
                if (!pmap_change_attr(va, size, mode))
                        return ((void *)va);

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