Merge pull request #1767 from giuseppe/change-formula-cpu-shares-conversion

cgroup: change conversion  from CPU shares to weight

Author: giuseppe

configure.ac

@@ -269,6 +269,41 @@ AS_IF([test "x$enable_criu" != "xno"], [
 
 ], [AC_MSG_NOTICE([CRIU support disabled per user request])])
 
+AC_MSG_CHECKING([for log2])
+AC_LINK_IFELSE([
+    AC_LANG_PROGRAM([
+        #include <math.h>
+        #include <stdlib.h>
+    ], [
+        double result = log2 ((double) rand ());
+        return (int) result;
+    ])
+], [
+    # log2 works without -lm (musl libc)
+    AC_MSG_RESULT([yes])
+    AC_DEFINE([HAVE_LOG2], [1], [Define if log2 is available])
+], [
+    # Try with -lm (glibc)
+    LIBS="$LIBS -lm"
+    AC_LINK_IFELSE([
+        AC_LANG_PROGRAM([
+            #include <math.h>
+            #include <stdlib.h>
+        ], [
+            double result = log2 ((double) rand ());
+            return (int) result;
+        ])
+    ], [
+        # log2 works with -lm
+        AC_MSG_RESULT([yes (with -lm)])
+        AC_DEFINE([HAVE_LOG2], [1], [Define if log2 is available])
+    ], [
+        # log2 not available - restore LIBS and fail
+        AC_MSG_RESULT([no])
+        AC_MSG_ERROR([*** log2 function is required but not found])
+    ])
+])
+
 FOUND_LIBS=$LIBS
 LIBS=""
 

crun.1

@@ -846,7 +846,10 @@ allbox;
 l l l l 
 l l l l .
 \fBOCI (x)\fP	\fBcgroup 2 value (y)\fP	\fBconversion\fP	\fBcomment\fP
-shares	cpu.weight	y = (1 + ((x - 2) * 9999) / 262142)	T{
+shares	cpu.weight	T{
+y=10^((log2(x)^2 + 125 * log2(x)) / 612.0 - 7.0 / 34.0)
+T}
+	T{
 convert from [2-262144] to [1-10000]
 T}
 period	cpu.max	y = x	T{

crun.1.md

@@ -712,11 +712,11 @@ they are converted when needed from the cgroup v1 configuration.
 
 ## CPU controller
 
-| OCI (x) | cgroup 2 value (y) | conversion  |  comment |
-|---|---|---|---|
-| shares | cpu.weight | y = (1 + ((x - 2) \* 9999) / 262142) | convert from [2-262144] to [1-10000]|
-| period | cpu.max | y = x| period and quota are written together|
-| quota | cpu.max | y = x| period and quota are written together|
+| OCI (x) | cgroup 2 value (y) | conversion                                              | comment                               |
+|---------|--------------------|---------------------------------------------------------|---------------------------------------|
+| shares  | cpu.weight         | y=10^((log2(x)^2 + 125 * log2(x)) / 612.0 - 7.0 / 34.0) | convert from [2-262144] to [1-10000]  |
+| period  | cpu.max            | y = x                                                   | period and quota are written together |
+| quota   | cpu.max            | y = x                                                   | period and quota are written together |
 
 ## blkio controller
 

src/libcrun/cgroup-internal.h

@@ -21,6 +21,9 @@
 #include "container.h"
 #include "utils.h"
 
+#include <stdint.h>
+#include <math.h>
+
 enum
 {
   CGROUP_MEMORY = 1 << 0,
@@ -76,8 +79,22 @@ int libcrun_cgroup_pause_unpause_path (const char *cgroup_path, const bool pause
 static inline uint64_t
 convert_shares_to_weight (uint64_t shares)
 {
-  /* convert linearly from 2-262144 to 1-10000.  */
-  return (1 + ((shares - 2) * 9999) / 262142);
+  double l, exponent;
+
+  /* The value of 0 means "unset".  */
+  if (shares == 0)
+    return 0;
+  if (shares <= 2)
+    return 1;
+  if (shares >= 262144)
+    return 10000;
+
+  l = log2 ((double) shares);
+
+  /* Quadratic function which fits min, max, and default.  */
+  exponent = (l * l + 125 * l) / 612.0 - 7.0 / 34.0;
+
+  return (uint64_t) ceil (pow (10, exponent));
 }
 
 int initialize_cpuset_subsystem (const char *path, libcrun_error_t *err);

tests/alpine-build/Dockerfile

@@ -1,7 +1,7 @@
 FROM alpine
 
 RUN apk add gcc automake autoconf libtool gettext pkgconf git make musl-dev \
-    python3 libcap-dev libseccomp-dev yajl-dev argp-standalone go-md2man
+    python3 libcap-dev libseccomp-dev yajl-dev argp-standalone go-md2man gperf
 
 COPY run-tests.sh /usr/local/bin
 

tests/test_resources.py

@@ -291,23 +291,26 @@ def test_resources_cpu_weight_systemd():
             sys.stderr.write("# found wrong CPUWeight for the systemd scope\n")
             return 1
 
-        run_crun_command(['update', '--cpu-share', '4321', cid])
-        # this is the expected cpu weight after the conversion from the CPUShares
-        expected_weight = "165"
+        for values in [(2, 1), (3, 2), (1024, 100), (260000, 9929), (262144, 10000)]:
+            cpu_shares = values[0]
+            # this is the expected cpu weight after the conversion from the CPUShares
+            expected_weight = str(values[1])
 
-        out = run_crun_command(["exec", cid, "/init", "cat", "/sys/fs/cgroup/cpu.weight"])
-        if expected_weight not in out:
-            sys.stderr.write("# found wrong CPUWeight %s for the container cgroup\n" % out)
-            return -1
+            run_crun_command(['update', '--cpu-share', str(cpu_shares), cid])
 
-        out = subprocess.check_output(['systemctl', 'show','-PCPUWeight', scope ], close_fds=False).decode().strip()
-        # as above
-        if out != expected_weight:
-            out = subprocess.check_output(['systemctl', '--user', 'show','-PCPUWeight', scope ], close_fds=False).decode().strip()
+            out = run_crun_command(["exec", cid, "/init", "cat", "/sys/fs/cgroup/cpu.weight"])
+            if expected_weight not in out:
+                sys.stderr.write("found wrong CPUWeight %s instead of %s for the container cgroup\n" % (out, expected_weight))
+                return -1
 
-        if out != expected_weight:
-            sys.stderr.write("# found wrong CPUWeight for the systemd scope\n")
-            return 1
+            out = subprocess.check_output(['systemctl', 'show','-PCPUWeight', scope ], close_fds=False).decode().strip()
+            # as above
+            if out != expected_weight:
+                out = subprocess.check_output(['systemctl', '--user', 'show','-PCPUWeight', scope ], close_fds=False).decode().strip()
+
+            if out != expected_weight:
+                sys.stderr.write("found wrong CPUWeight for the systemd scope\n")
+                return 1
     finally:
         if cid is not None:
             run_crun_command(["delete", "-f", cid])