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authorSiddhesh Poyarekar <siddhesh@sourceware.org>2021-02-05 13:18:58 +0530
committerSiddhesh Poyarekar <siddhesh@sourceware.org>2021-02-10 19:08:33 +0530
commit61117bfa1b08ca048e6512c0652c568300fedf6a (patch)
treed752f7a8eec0c3a174c42f73f1e7927616d6d073 /manual
parente604a5e4bb61267c58e6b6179209efe74ab5f675 (diff)
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tunables: Simplify TUNABLE_SET interface
The TUNABLE_SET interface took a primitive C type argument, which resulted in inconsistent type conversions internally due to incorrect dereferencing of types, especialy on 32-bit architectures. This change simplifies the TUNABLE setting logic along with the interfaces. Now all numeric tunable values are stored as signed numbers in tunable_num_t, which is intmax_t. All calls to set tunables cast the input value to its primitive type and then to tunable_num_t for storage. This relies on gcc-specific (although I suspect other compilers woul also do the same) unsigned to signed integer conversion semantics, i.e. the bit pattern is conserved. The reverse conversion is guaranteed by the standard.
Diffstat (limited to 'manual')
-rw-r--r--manual/README.tunables16
1 files changed, 7 insertions, 9 deletions
diff --git a/manual/README.tunables b/manual/README.tunables
index d8c768a..605ddd7 100644
--- a/manual/README.tunables
+++ b/manual/README.tunables
@@ -98,17 +98,16 @@ where it can expect the tunable value to be passed in VALP.
Tunables in the module can be updated using:
- TUNABLE_SET (check, int32_t, val)
+ TUNABLE_SET (check, val)
-where 'check' is the tunable name, 'int32_t' is the C type of the tunable and
-'val' is a value of same type.
+where 'check' is the tunable name and 'val' is a value of same type.
To get and set tunables in a different namespace from that module, use the full
form of the macros as follows:
val = TUNABLE_GET_FULL (glibc, cpu, hwcap_mask, uint64_t, NULL)
- TUNABLE_SET_FULL (glibc, cpu, hwcap_mask, uint64_t, val)
+ TUNABLE_SET_FULL (glibc, cpu, hwcap_mask, val)
where 'glibc' is the top namespace, 'cpu' is the tunable namespace and the
remaining arguments are the same as the short form macros.
@@ -116,18 +115,17 @@ remaining arguments are the same as the short form macros.
The minimum and maximum values can updated together with the tunable value
using:
- TUNABLE_SET_WITH_BOUNDS (check, int32_t, val, min, max)
+ TUNABLE_SET_WITH_BOUNDS (check, val, min, max)
-where 'check' is the tunable name, 'int32_t' is the C type of the tunable,
-'val' is a value of same type, 'min' and 'max' are the minimum and maximum
-values of the tunable.
+where 'check' is the tunable name, 'val' is a value of same type, 'min' and
+'max' are the minimum and maximum values of the tunable.
To set the minimum and maximum values of tunables in a different namespace
from that module, use the full form of the macros as follows:
val = TUNABLE_GET_FULL (glibc, cpu, hwcap_mask, uint64_t, NULL)
- TUNABLE_SET_WITH_BOUNDS_FULL (glibc, cpu, hwcap_mask, uint64_t, val, min, max)
+ TUNABLE_SET_WITH_BOUNDS_FULL (glibc, cpu, hwcap_mask, val, min, max)
where 'glibc' is the top namespace, 'cpu' is the tunable namespace and the
remaining arguments are the same as the short form macros.