Date: Sun, 8 Jul 2012 21:05:16 +1000 From: Peter Jeremy <peter@rulingia.com> To: freebsd-hackers@freebsd.org Subject: Re: contigmalloc() breaking Xorg Message-ID: <20120708110516.GA38312@server.rulingia.com> In-Reply-To: <20120703111753.GB72292@server.rulingia.com> References: <20120703111753.GB72292@server.rulingia.com>
next in thread | previous in thread | raw e-mail | index | archive | help
--/9DWx/yDrRhgMJTb Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2012-Jul-03 21:17:53 +1000, Peter Jeremy <peter@server.rulingia.com> wro= te: >I have a reasonably recent 8-stable/amd64 system (r237444) with a "ATI >Radeon HD 2400 Pro", xorg-server-1.10.6,1 and xf86-video-ati-6.14.3_1 >8GB RAM and ZFS. I'm seeing fairly consistent problems with Xorg =2E.. >How difficult would it be to modify bus_dmamem_alloc() [at least on >x86] to handle multi-segment allocations? I think I've managed to create an amd64 bus_dmamem_alloc() that allows page-sized allocations as long as no boundary condition is specified and no more than page-sized alignment is required (porting it to other architectures would be trivial). I've given it a quick whirl inside a VBox and no smoke came out but I'd appreciate someone with a better understanding of bus_dma(9) and vm/vm_contig.c giving http://www.rulingia.com/bugs/patch-wiredmalloc a once-over. Note that this patch is against 8.x but there's only a trivial difference to head. BTW, the comment in busdma_machdep.c:bus_dmamem_alloc() * XXX Use Contigmalloc until it is merged into this facility * and handles multi-seg allocations. Nobody is doing * multi-seg allocations yet though. * XXX Certain AGP hardware does. does not appear to be accurate. Apart from drm, quite a few drivers call bus_dma_tag_create(9) with multiple segments and also call bus_dmamem_alloc(9) [though I haven't verified that the calls share the same bus_dma_tag, so I can't be absolutely certain]. BTW(2): Whilst studying busdma_machdep.c for arm and mips, I've noticed they appear to potentially allocate substantial kernel stack under some conditions as several bus_dma(9) functions include: bus_dma_segment_t dm_segments[dmat->nsegments]; What prevents this overflowing the kernel stack? --=20 Peter Jeremy --/9DWx/yDrRhgMJTb Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iEYEARECAAYFAk/5aWwACgkQ/opHv/APuIdzaACaA4AO/KTUaGipf+W8ON6dy6ud 7WIAoMNon9i8PrZ+k72+fX+keyE4m87i =nFuQ -----END PGP SIGNATURE----- --/9DWx/yDrRhgMJTb--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20120708110516.GA38312>