On 12/11/17 5:26 AM, Eugene Grosbein wrote: > On 11.12.2017 16:19, Konstantin Belousov wrote: >> On Mon, Dec 11, 2017 at 04:32:37AM +0000, Conrad Meyer wrote: >>> Author: cem >>> Date: Mon Dec 11 04:32:37 2017 >>> New Revision: 326758 >>> URL: https://svnweb.freebsd.org/changeset/base/326758 >>> >>> Log: >>> i386: Bump KSTACK_PAGES default to match amd64 >> i386 is not amd64, the change is wrong. >> >> i386 has the word size two times smaller than amd64, which makes typical >> frame smaller by 30-40% over same code on amd64. Also i386 has much >> smaller available KVA size (tens of MB) and KVA fragmentation is both >> more severe and more fatal due to this. I expect that your change will >> make any non-trivial load which creates enough threads to either fail >> randomly or deadlock. >> >> If somebody tries to fit large load onto i386 machine, he must know what to >> do and how to configure the kernel to adapt to the load (which does not >> require the recompilation). > > Its very easy to get kernel stack overflow with 11-STABLE/i386 > without any significant load due to abuse of kernel stack in many kernel > subsystems > as shown in the https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=219476 > > Contrary, "enough threads" seems to be very non-trivial number of threads > and pretty unusual load pattern for i386 as I run several such systems > with kern.kstack_pages=4 for quite long time and have no problems. > No random fails, no deadlocks. And with 2 pages only 11-STABLE/i386 is just > unusable > if one utilizes SCTP, IPv6, some WiFi connectivity, IPSEC or even very small > ZFS pool. > > I still wonder if there is really such load pattern that creates "enough > threads" > for i386 to make 4-pages stack troublesome.
I suspect two things are at play in running out of stack in 10.x and later. 1) Usage of XSAVE for AVX, etc. state uses more of the kstack (as kib@ alludes to), and 2) clang. Certainly for MIPS I have found that compiling with clang instead of gcc for mips64 gives a kernel that panics for stack overflow for any use of NFS. It might be that this is due to something MIPS-specific, but it might be worthwhile retesting with kstack_pages=2 and building the kernel with CROSS_TOOLCHAIN=i386-gcc after installing the appropriate package. For people wanting to use 32-bit binaries on a modern x86 box, we should probably add support for the x32 ABI permitting you to use 32-bit pointers but with the full complement of 64-bit registers (and still using the 64-bit kernel so there is not KVA pressure for the kernel itself). -- John Baldwin _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
