The four cpumasks cpu_{possible,online,present,active}_bits are exposed
readonly via the corresponding const variables cpu_xyz_mask. But they are
also accessible for arbitrary writing via the exposed functions
set_cpu_xyz. There's quite a bit of code throughout the kernel which
iterates over or otherwise accesses these bitmaps, and having the access
go via the cpu_xyz_mask variables is nowadays [1] simply a useless
indirection.
It may be that any problem in CS can be solved by an extra level of
indirection, but that doesn't mean every extra indirection solves a
problem. In this case, it even necessitates some minor ugliness (see
4/6).
Patch 1/6 is new in v2, and fixes a build failure on ppc by renaming a
struct member, to avoid problems when the identifier cpu_online_mask
becomes a macro later in the series. The next four patches eliminate the
cpu_xyz_mask variables by simply exposing the actual bitmaps, after
renaming them to discourage direct access - that still happens through
cpu_xyz_mask, which are now simply macros with the same type and value as
they used to have.
After that, there's no longer any reason to have the setter functions be
out-of-line: The boolean parameter is almost always a literal true or
false, so by making them static inlines they will usually compile to one
or two instructions.
For a defconfig build on x86_64, bloat-o-meter says we save ~3000 bytes.
We also save a little stack (stackdelta says 127 functions have a 16 byte
smaller stack frame, while two grow by that amount). Mostly because, when
iterating over the mask, gcc typically loads the value of cpu_xyz_mask
into a callee-saved register and from there into %rdi before each
find_next_bit call - now it can just load the appropriate immediate
address into %rdi before each call.
[1] See Rusty's kind explanation
http://thread.gmane.org/gmane.linux.kernel/2047078/focus=2047722 for
some historic context.
This patch (of 6):
As preparation for eliminating the indirect access to the various global
cpu_*_bits bitmaps via the pointer variables cpu_*_mask, rename the
cpu_online_mask member of struct fadump_crash_info_header to simply
online_mask, thus allowing cpu_online_mask to become a macro.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This patch introduces an sysfs interface '/sys/kernel/fadump_release_mem' to
invalidate the last fadump registration, invalidate '/proc/vmcore', release
the reserved memory for general use and re-register for future kernel dump.
Once the dump is copied to the disk, unlike phyp dump, the userspace tool
can release all the memory reserved for dump with one single operation of
echo 1 to '/sys/kernel/fadump_release_mem'.
Release the reserved memory region excluding the size of the memory required
for future kernel dump registration. And therefore, unlike kdump, Fadump
doesn't need a 2nd reboot to get back the system to the production
configuration.
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
When registered for firmware assisted dump on powerpc, firmware preserves
the registers for the active CPUs during a system crash. This patch reads
the cpu register data stored in Firmware-assisted dump format (except for
crashing cpu) and converts it into elf notes and updates the PT_NOTE program
header accordingly. The exact register state for crashing cpu is saved to
fadump crash info structure in scratch area during crash_fadump() and read
during second kernel boot.
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Build the crash memory range list by traversing through system memory during
the first kernel before we register for firmware-assisted dump. After the
successful dump registration, initialize the elfcore header and populate
PT_LOAD program headers with crash memory ranges. The elfcore header is
saved in the scratch area within the reserved memory. The scratch area starts
at the end of the memory reserved for saving RMR region contents. The
scratch area contains fadump crash info structure that contains magic number
for fadump validation and physical address where the eflcore header can be
found. This structure will also be used to pass some important crash info
data to the second kernel which will help second kernel to populate ELF core
header with correct data before it gets exported through /proc/vmcore. Since
the firmware preserves the entire partition memory at the time of crash the
contents of the scratch area will be preserved till second kernel boot.
Since the memory dump exported through /proc/vmcore is in ELF format similar
to kdump, it will help us to reuse the kdump infrastructure for dump capture
and filtering. Unlike phyp dump, userspace tool does not need to refer any
sysfs interface while reading /proc/vmcore.
NOTE: The current design implementation does not address a possibility of
introducing additional fields (in future) to this structure without affecting
compatibility. It's on TODO list to come up with better approach to
address this.
Reserved dump area start => +-------------------------------------+
| CPU state dump data |
+-------------------------------------+
| HPTE region data |
+-------------------------------------+
| RMR region data |
Scratch area start => +-------------------------------------+
| fadump crash info structure { |
| magic nummber |
+------|---- elfcorehdr_addr |
| | } |
+----> +-------------------------------------+
| ELF core header |
Reserved dump area end => +-------------------------------------+
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
On 2012-02-20 11:02:51 Mon, Paul Mackerras wrote:
> On Thu, Feb 16, 2012 at 04:44:30PM +0530, Mahesh J Salgaonkar wrote:
>
> If I have read the code correctly, we are going to get this printk on
> non-pSeries machines or on older pSeries machines, even if the user
> has not put the fadump=on option on the kernel command line. The
> printk will be annoying since there is no actual error condition. It
> seems to me that the condition for the printk should include
> fw_dump.fadump_enabled. In other words you should probably add
>
> if (!fw_dump.fadump_enabled)
> return 0;
>
> at the beginning of the function.
Hi Paul,
Thanks for pointing it out. Please find the updated patch below.
The existing patches above this (4/10 through 10/10) cleanly applies
on this update.
Thanks,
-Mahesh.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reserve the memory during early boot to preserve CPU state data, HPTE region
and RMA (real mode area) region data in case of kernel crash. At the time of
crash, powerpc firmware will store CPU state data, HPTE region data and move
RMA region data to the reserved memory area.
If the firmware-assisted dump fails to reserve the memory, then fallback
to existing kexec-based kdump.
Most of the code implementation to reserve memory has been
adapted from phyp assisted dump implementation written by Linas Vepstas
and Manish Ahuja
This patch also introduces a config option CONFIG_FA_DUMP for firmware
assisted dump feature on Powerpc (ppc64) architecture.
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Rasmus Villemoes
Hari Bathini
Rashika Kheria
Mahesh Salgaonkar