i was profiling the scheduler on x86 and noticed some overhead related
to SECCOMP, and indeed, SECCOMP runs disable_tsc() at _every_
context-switch:
if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr))
handle_io_bitmap(next, tss);
disable_tsc(prev_p, next_p);
return prev_p;
these are a couple of instructions in the hottest scheduler codepath!
x86_64 already removed disable_tsc() from switch_to(), but i think the
right solution is to turn SECCOMP off by default.
besides the runtime overhead, there are a couple of other reasons as
well why this should be done:
- CONFIG_SECCOMP=y adds 836 bytes of bloat to the kernel:
text data bss dec hex filename
4185360 867112 391012 5443484 530f9c vmlinux-noseccomp
4185992 867316 391012 5444320 5312e0 vmlinux-seccomp
- virtually nobody seems to be using it (but cpushare.com, which seems
pretty inactive)
- users/distributions can still turn it on if they want it
- http://www.cpushare.com/legal seems to suggest that it is pursuing a
software patent to utilize the seccomp concept in a distributed
environment, and seems to give a promise that 'end users' will not be
affected by that patent. How about non-end-users [i.e. server-side]?
Has the Linux kernel become a vehicle for a propriety server-side
feature, with every Linux user paying the price of it?
so the patch below just does the minimal common-sense change: turn it
off by default.
Ingo
--
turn SECCOMP off by default - it adds runtime per-context-switch
overhead on x86, and bloats the kernel.
Signed-off-by: Ingo Molnar <[email protected]>
----
arch/i386/Kconfig | 2 +-
arch/mips/Kconfig | 2 +-
arch/powerpc/Kconfig | 2 +-
arch/ppc/Kconfig | 2 +-
arch/sparc64/Kconfig | 2 +-
arch/x86_64/Kconfig | 2 +-
6 files changed, 6 insertions(+), 6 deletions(-)
Index: linux/arch/i386/Kconfig
===================================================================
--- linux.orig/arch/i386/Kconfig
+++ linux/arch/i386/Kconfig
@@ -637,7 +637,7 @@ config REGPARM
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS
- default y
+ default n
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their
Index: linux/arch/mips/Kconfig
===================================================================
--- linux.orig/arch/mips/Kconfig
+++ linux/arch/mips/Kconfig
@@ -1787,7 +1787,7 @@ config BINFMT_ELF32
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS && BROKEN
- default y
+ default n
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their
Index: linux/arch/powerpc/Kconfig
===================================================================
--- linux.orig/arch/powerpc/Kconfig
+++ linux/arch/powerpc/Kconfig
@@ -666,7 +666,7 @@ endif
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS
- default y
+ default n
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their
Index: linux/arch/ppc/Kconfig
===================================================================
--- linux.orig/arch/ppc/Kconfig
+++ linux/arch/ppc/Kconfig
@@ -1127,7 +1127,7 @@ endif
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS
- default y
+ default n
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their
Index: linux/arch/sparc64/Kconfig
===================================================================
--- linux.orig/arch/sparc64/Kconfig
+++ linux/arch/sparc64/Kconfig
@@ -64,7 +64,7 @@ endchoice
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS
- default y
+ default n
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their
Index: linux/arch/x86_64/Kconfig
===================================================================
--- linux.orig/arch/x86_64/Kconfig
+++ linux/arch/x86_64/Kconfig
@@ -466,7 +466,7 @@ config PHYSICAL_START
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS
- default y
+ default n
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their
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