Intel KMS: a memory problem

[Luca Pizzamiglio]

On 06/13/12 13:26, Konstantin Belousov wrote:
> On Wed, Jun 13, 2012 at 12:40:19PM +0200, Luca Pizzamiglio wrote:
>> Hi people,
>>
>> I'm using 9-RELENG with KMS and the last port updated on a SandyBridge
>> platform (Intel Graphics)
>> With a quite simple openGL application, a panic occurred:
>>
>> panic: pmap_mapdev: Couldn't alloc kernel virtual memory
>> Tracing pid 944 tid 100105 td 0xca85c8a0
>> kdb_enter(c0ffe535,c0ffe535,c103dcff,efa62ac0,1,...) at kdb_enter+0x3a
>> panic(c103dcff,5000,c9879151,0,c1a02000,...) at panic+0x18c
>> pmap_mapdev_attr(c1a02000,4800,1,1,c911d980,...) at pmap_mapdev_attr+0x7e
>> i915_gem_obj_io(2d014008,0,4800,0,0,...) at i915_gem_obj_io+0x513
>> i915_gem_pwrite_ioctl(c9925800,ca827120,ca871300,c0a78b5b,efa62bd4,...)
>> at i915_gem_pwrite_ioctl+0x4b
>> drm_ioctl(c97e0400,8020645d,ca827120,3,ca85c8a0,...) at drm_ioctl+0x2d8
>> devfs_ioctl_f(c91cb850,8020645d,ca827120,c91b5e80,ca85c8a0,...) at
>> devfs_ioctl_f+0x10a
>> kern_ioctl(ca85c8a0,4,8020645d,ca827120,a62ccc,...) at kern_ioctl+0x2a0
>> sys_ioctl(ca85c8a0,efa62ccc,c67c4c80,293d3b4e,1,...) at sys_ioctl+0x134
>> syscall(efa62d08) at syscall+0x34a
>> Xint0x80_syscall() at Xint0x80_syscall+0x21
>> --- syscall (54, FreeBSD ELF32, sys_ioctl), eip = 0x293d5b93, esp =
>> 0xbfbf7f4c, ebp = 0xbfbf7f68 ---
>>
>> I tried to increase vm.kmem_size and vm.kmem_size_max to 512M, but the
>> problem persists.
>>
>> Any easy idea or workaround?
>> In the meanwhile, I'll try to investigate this problem deeper.
>
> You are probably first who run 32bit kernel on SandyBridge + GEMified
> i915 driver.
>
>  From the trace you provided it seems that kernel was unable to find
> a free area in KVA for 5 consequtive pages. I would think that you have
> relatively high fragmentation of KVA. What load on machine is ?
>
> Actually, quite some time ago, i915_gem_gtt_write() did mapped gtt
> page by page, instead of mapping the whole range of pages undergoing i/o.
> I was pointed out that this was major performance bootleneck for GTT
> mapped objects. It might be reasonable to restore the slow mode for
> 32bit kernels, since people running such kernels on SandyBridge definitely
> do not care about performance.
>

Hi Konstantin,
Thanks for the quick reply!
yes, maybe I'm the first using 32bit architecture on SandyBridge, but 
for some internal conflicts (human ones) I should use 32 bit version and 
performance is an important topic.
It's quite strange what are you saying about KVA fragmentation, the load 
of the machine is really low < 0.3; test scenario is: boot, starting X 
with twm and launching our openGL application.. after a couple of 
minutes, it panics. The openGL application draw a black screen and some 
lines to show performance indexes, like CPU percentage usage, time per 
frame, and so on. CPU percentage is about 7-9%.
The system has 4 GB of memory, but only 3GB are addressable.
Any idea how could I monitor memory fragmentation?

I would like to try PAE extension to address more memory or use 64 bit 
world with the 32 bit compatibility layer. PAE extension is easy to 
test, but for 64bit I need to delete&reinstall&recompile everything...

Thanks in advance for the help

Best regards,
Luca