On Sat, 31 Mar 2018, Konstantin Belousov wrote:
the change to provide full 4G of address space for both kernel and
user on i386 is ready to land. The motivation for the work was to both
mitigate Meltdown on i386, and to give more breazing space for still
used 32bit architecture. The patch was tested by Peter Holm, and I am
satisfied with the code.
If you use i386 with HEAD, I recommend you to apply the patch from
https://reviews.freebsd.org/D14633
and report any regressions before the commit, not after. Unless
a significant issue is reported, I plan to commit the change somewhere
at Wed/Thu next week.
Also I welcome patch comments and reviews.
It crashes at boot time in getmemsize() unless booted with loader which
I don't want to use.
It is much slower, and I couldn't find an option to turn it off.
For makeworld, the system time is slightly more than doubled, the user
time is increased by 16%, and the real time is increased by 21%.
On amd64, turning off pti and not having ibrs gives almost no increase
in makeworld times relative to old versions, and pti only costs about
5% IIRC.
Makeworld is not very syscall-intensive. netblast is very syscall-intensive,
and its throughput is down by a factor of 5 (660/136 = 4.9, 1331/242 = 5.5).
netblast 127.0.0.1 5001 5 10 (localhost, port 5001, 5-byte tinygrams for 10 s):
537 kpps sent, 0 kpps dropped # before this patch (CPU use 1.3)
136 kpps sent, 0 kpps dropped # after (CPU use 2.1)
(Pure software overheads. It uses 1.6 times as much CPU to go 4 times
slower).
netblast 192.168.2.8 (low end PCI33 lem on low latency 1 Gbps LAN)
275 kpps sent, 1045 kpps dropped # before (CPU use 1.3)
245 kpps sent, 0 kpps dropped # after (CPU use 1.3)
(The hardware can't do anywhere near line rate of ~1500 kpps, so this
becomes a benchmark of syscalls and dropping packets. The change makes
FreeBSD so slow that 8 CPUs at 4.08 can't saturate a low end PCI33 NIC
(the hardware saturates at about 282 kpps for tx and about 400 kpps for
rx)).
netblast 192.168.2.8 (low end PCIe em on low latency 1 Gbps LAN)
1316 kpps sent, 3 kpps dropped # before (CPU use 1.6)
243 kpps sent, 0 kpps dropped # after (CPU use 1.2)
This is seriously slower for the most useful case. It reduces a system
that could almost reach line rate using about 2 of 8 CPUs at 4 GHz to
one that that is slower than with 1 CPU at 2 GHz (the latter saturates
in software at about 640 kpps in old versions of FreeBSD at at about
400 kpps in -current).
Initial debugging of the crash: it crashes on the first pmap_kenter()
in getmemsize(). I configure debug.late_console to 0. That works,
and without it getmemsize() can't even be debugged since it is after
console initialization and ddb entry with -d.
In getmemsize(), of course all the preload calls return 0 and smapbase is
NULL. Then vm86 bios calls work and give basemem = 0x276. Then
basemem_setup() is called and it returns. Then pmap_kenter() is called
and it crashes:
Stopped at getmemsize+0xb3: pushl $0x1000
Stopped at getmemsize+0xb8: pushl $0x1000
Stopped at getmemsize+0xbd: call pmap_kenter
Stopped at pmap_kenter: pushl %ebp
Stopped at pmap_kenter+0x1: movl %esp,%ebp
Stopped at pmap_kenter+0x3: movl 0x8(%ebp),%eax
Stopped at pmap_kenter+0x6: shrl $0xc,%eax
Stopped at pmap_kenter+0x9: movl 0xc(%ebp),%edx
Stopped at pmap_kenter+0xc: orl $0x3,%edx
Stopped at pmap_kenter+0xf: movl %edx,PTmap(,%eax,4)
The last instruction crashes because PTmap is not mapped at this point:
db> p/x $edx
1003
db> p/x PTmap
ff800000
db> p/x $eax
1
db> x/x PTmap
PTmap:KDB: reentering
KDB: stack backtrace:
db_trace_self_wrapper(cec5cb,1420a04,c6de83,1420978,1,...) at
db_trace_self_wrapper+0x24/frame 0x142095c
kdb_reenter(1420978,1,ff80003a,1420998,8f1419,...) at kdb_reenter+0x24/frame
0x1420968
trap(1420a10) at trap+0xa0/frame 0x1420a04
calltrap() at calltrap+0x8/frame 0x1420a04
--- trap 0xc, eip = 0xc5c394, esp = 0x1420a50, ebp = 0x1420a88 ---
db_read_bytes(ff800001,3,1420aa0) at db_read_bytes+0x29/frame 0x1420a88
db_get_value(ff800000,4,0,0,d2d304,...) at db_get_value+0x20/frame 0x1420ab4
db_examine(ff800000,1,ffffffff,1420b00) at db_examine+0x144/frame 0x1420ae4
db_command(cb1d99,1420be4,8f0f01,d1d28a,0,...) at db_command+0x20a/frame
0x1420b90
db_command_loop(d1d28a,0,1420bac,1420b9c,1420be4,...) at
db_command_loop+0x55/frame 0x1420b9c
db_trap(a,ffff4ff0,1,1,80046,...) at db_trap+0xe1/frame 0x1420be4
kdb_trap(a,ffff4ff0,1420cc4) at kdb_trap+0xb1/frame 0x1420c10
trap(1420cc4) at trap+0x523/frame 0x1420cb8
calltrap() at calltrap+0x8/frame 0x1420cb8
--- trap 0xa, eip = 0xc65a4a, esp = 0x1420d04, ebp = 0x1420d04 ---
pmap_kenter(1000,1000,1429000,8efe13,0,...) at pmap_kenter+0xf/frame 0x1420d04
getmemsize(1,5a8807ff,ee,59a80097,ee,...) at getmemsize+0xc2/frame 0x1420fc4
init386(1428000) at init386+0x2bb/frame 0x1420ff4
btext() at btext+0x55
*** error reading from address ff800000 ***
--More-- KDB: reentering
KDB: stack backtrace:
db_trace_self_wrapper(cec5cb,1420ab4,8ee255,cb1923,ff800000,...) at
db_trace_self_wrapper+0x24/frame 0x1420a7c
kdb_reenter(cb1923,ff800000,0) at kdb_reenter+0x24/frame 0x1420a88
db_get_value(ff800000,4,0,0,d2d304,...) at db_get_value+0x3a/frame 0x1420ab4
db_examine(ff800000,1,ffffffff,1420b00) at db_examine+0x144/frame 0x1420ae4
db_command(cb1d99,1420be4,8f0f01,d1d28a,0,...) at db_command+0x20a/frame
0x1420b90
db_command_loop(d1d28a,0,1420bac,1420b9c,1420be4,...) at
db_command_loop+0x55/frame 0x1420b9c
db_trap(a,ffff4ff0,1,1,80046,...) at db_trap+0xe1/frame 0x1420be4
kdb_trap(a,ffff4ff0,1420cc4) at kdb_trap+0xb1/frame 0x1420c10
trap(1420cc4) at trap+0x523/frame 0x1420cb8
calltrap() at calltrap+0x8/frame 0x1420cb8
--- trap 0xa, eip = 0xc65a4a, esp = 0x1420d04, ebp = 0x1420d04 ---
pmap_kenter(1000,1000,1429000,8efe13,0,...) at pmap_kenter+0xf/frame 0x1420d04
getmemsize(1,5a8807ff,ee,59a80097,ee,...) at getmemsize+0xc2/frame 0x1420fc4
init386(1428000) at init386+0x2bb/frame 0x1420ff4
btext() at btext+0x55
db>
Bruce
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