[PULL,21/41] include/hw/qdev-properties: Shrink struct Property

Commit Message

Paolo Bonzini Dec. 19, 2024, 8:32 a.m. UTC

From: Richard Henderson <[e-mail]>

Before, via pahole:

arm32, a 32-bit host which aligns uint64_t:

struct Property {
        const char  *              name;                 /*     0     4 */
        const PropertyInfo  *      info;                 /*     4     4 */
        ptrdiff_t                  offset;               /*     8     4 */
        uint8_t                    bitnr;                /*    12     1 */
        /* XXX 3 bytes hole, try to pack */
        uint64_t                   bitmask;              /*    16     8 */
        _Bool                      set_default;          /*    24     1 */
        /* XXX 7 bytes hole, try to pack */
        union {
                int64_t            i;                    /*    32     8 */
                uint64_t           u;                    /*    32     8 */
        } defval;                                        /*    32     8 */
        int                        arrayoffset;          /*    40     4 */
        const PropertyInfo  *      arrayinfo;            /*    44     4 */
        int                        arrayfieldsize;       /*    48     4 */
        const char  *              link_type;            /*    52     4 */
        /* size: 56, cachelines: 1, members: 11 */
        /* sum members: 46, holes: 2, sum holes: 10 */
};

arm64, an arbitrary 64-bit host:

struct Property {
        const char  *              name;                 /*     0     8 */
        const PropertyInfo  *      info;                 /*     8     8 */
        ptrdiff_t                  offset;               /*    16     8 */
        uint8_t                    bitnr;                /*    24     1 */
        /* XXX 7 bytes hole, try to pack */
        uint64_t                   bitmask;              /*    32     8 */
        _Bool                      set_default;          /*    40     1 */
        /* XXX 7 bytes hole, try to pack */
        union {
                int64_t            i;                    /*    48     8 */
                uint64_t           u;                    /*    48     8 */
        } defval;                                        /*    48     8 */
        int                        arrayoffset;          /*    56     4 */
        /* XXX 4 bytes hole, try to pack */
        const PropertyInfo  *      arrayinfo;            /*    64     8 */
        int                        arrayfieldsize;       /*    72     4 */
        /* XXX 4 bytes hole, try to pack */
        const char  *              link_type;            /*    80     8 */
        /* size: 88, cachelines: 2, members: 11 */
        /* sum members: 66, holes: 4, sum holes: 22 */
};

Afterward there are no holes in either structure.
For arm32, size 48, padding 2, saved 8 bytes.
For arm64, size 72, padding 6, saved 16 bytes.

Saves 20k from qemu-system-aarch64 on a 64-bit host.

Signed-off-by: Richard Henderson <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Paolo Bonzini <[e-mail]>
---
 include/hw/qdev-properties.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Patch

diff --git a/include/hw/qdev-properties.h b/include/hw/qdev-properties.h
index ef3fd7b4ae2..3680cd239fb 100644
--- a/include/hw/qdev-properties.h
+++ b/include/hw/qdev-properties.h
@@ -16,17 +16,17 @@  struct Property {
     const char   *name;
     const PropertyInfo *info;
     ptrdiff_t    offset;
-    uint8_t      bitnr;
+    const char   *link_type;
     uint64_t     bitmask;
-    bool         set_default;
     union {
         int64_t i;
         uint64_t u;
     } defval;
-    int          arrayoffset;
     const PropertyInfo *arrayinfo;
+    int          arrayoffset;
     int          arrayfieldsize;
-    const char   *link_type;
+    uint8_t      bitnr;
+    bool         set_default;
 };
 
 struct PropertyInfo {