Re: [PATCH v3] contrib/plugins: Add a plugin to generate basic block vectors

[Pierrick Bouvier <pierrick.bouvier@linaro.org>]

On 8/15/24 23:05, Akihiko Odaki wrote:
> SimPoint is a widely used tool to find the ideal microarchitecture
> simulation points so Valgrind[2] and Pin[3] support generating basic
> block vectors for use with them. Let's add a corresponding plugin to
> QEMU too.
> 
> Note that this plugin has a different goal with tests/plugin/bb.c.
> 
> This plugin creates a vector for each constant interval instead of
> counting the execution of basic blocks for the entire run and able to
> describe the change of execution behavior. Its output is also
> syntactically simple and better suited for parsing, while the output of
> tests/plugin/bb.c is more human-readable.
> 
> [1] https://cseweb.ucsd.edu/~calder/simpoint/
> [2] https://valgrind.org/docs/manual/bbv-manual.html
> [3] https://www.intel.com/content/www/us/en/developer/articles/tool/pin-a-dynamic-binary-instrumentation-tool.html
> 
> Signed-off-by: Yotaro Nada <yotaro.nada@gmail.com>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
> Changes in v3:
> - Protect the entire operation with bbs in vcpu_tb_trans().
> - Reduce memory allocations.
> - Link to v2: https://lore.kernel.org/r/20240815-bb-v2-1-6222ee98297b@daynix.com
> 
> Changes in v2:
> - Merged files variable into the global scoreboard.
> - Added a lock for bbs.
> - Added a summary to contrib/plugins/bbv.c.
> - Rebased.
> - Link to v1: https://lore.kernel.org/r/20240813-bb-v1-1-effbb77daebf@daynix.com
> ---
>   docs/about/emulation.rst |  30 +++++++++
>   contrib/plugins/bbv.c    | 158 +++++++++++++++++++++++++++++++++++++++++++++++
>   contrib/plugins/Makefile |   1 +
>   3 files changed, 189 insertions(+)
> 
> diff --git a/docs/about/emulation.rst b/docs/about/emulation.rst
> index c03033e4e956..72d7846ab6f8 100644
> --- a/docs/about/emulation.rst
> +++ b/docs/about/emulation.rst
> @@ -381,6 +381,36 @@ run::
>     160          1      0
>     135          1      0
>   
> +Basic Block Vectors
> +...................
> +
> +``contrib/plugins/bbv.c``
> +
> +The bbv plugin allows you to generate basic block vectors for use with the
> +`SimPoint <https://cseweb.ucsd.edu/~calder/simpoint/>`__ analysis tool.
> +
> +.. list-table:: Basic block vectors arguments
> +  :widths: 20 80
> +  :header-rows: 1
> +
> +  * - Option
> +    - Description
> +  * - interval=N
> +    - The interval to generate a basic block vector specified by the number of
> +      instructions (Default: N = 100000000)
> +  * - outfile=PATH
> +    - The path to output files.
> +      It will be suffixed with ``.N.bb`` where ``N`` is a vCPU index.
> +
> +Example::
> +
> +  $ qemu-aarch64 \
> +    -plugin contrib/plugins/libbbv.so,interval=100,outfile=sha1 \
> +    tests/tcg/aarch64-linux-user/sha1
> +  SHA1=15dd99a1991e0b3826fede3deffc1feba42278e6
> +  $ du sha1.0.bb
> +  23128   sha1.0.bb
> +
>   Hot Blocks
>   ..........
>   
> diff --git a/contrib/plugins/bbv.c b/contrib/plugins/bbv.c
> new file mode 100644
> index 000000000000..a5256517dd44
> --- /dev/null
> +++ b/contrib/plugins/bbv.c
> @@ -0,0 +1,158 @@
> +/*
> + * Generate basic block vectors for use with the SimPoint analysis tool.
> + * SimPoint: https://cseweb.ucsd.edu/~calder/simpoint/
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include <stdio.h>
> +#include <glib.h>
> +
> +#include <qemu-plugin.h>
> +
> +typedef struct Bb {
> +    uint64_t vaddr;
> +    struct qemu_plugin_scoreboard *count;
> +    unsigned int index;
> +} Bb;
> +
> +typedef struct Vcpu {
> +    uint64_t count;
> +    FILE *file;
> +} Vcpu;
> +
> +QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
> +static GHashTable *bbs;
> +static GRWLock bbs_lock;
> +static char *filename;
> +static struct qemu_plugin_scoreboard *vcpus;
> +static uint64_t interval = 100000000;
> +
> +static void plugin_exit(qemu_plugin_id_t id, void *p)
> +{
> +    for (int i = 0; i < qemu_plugin_num_vcpus(); i++) {
> +        fclose(((Vcpu *)qemu_plugin_scoreboard_find(vcpus, i))->file);
> +    }
> +
> +    g_hash_table_unref(bbs);
> +    g_free(filename);
> +    qemu_plugin_scoreboard_free(vcpus);
> +}
> +
> +static void free_bb(void *data)
> +{
> +    qemu_plugin_scoreboard_free(((Bb *)data)->count);
> +    g_free(data);
> +}
> +
> +static qemu_plugin_u64 count_u64(void)
> +{
> +    return qemu_plugin_scoreboard_u64_in_struct(vcpus, Vcpu, count);
> +}
> +
> +static qemu_plugin_u64 bb_count_u64(Bb *bb)
> +{
> +    return qemu_plugin_scoreboard_u64(bb->count);
> +}
> +
> +static void vcpu_init(qemu_plugin_id_t id, unsigned int vcpu_index)
> +{
> +    g_autofree gchar *vcpu_filename = NULL;
> +    Vcpu *vcpu = qemu_plugin_scoreboard_find(vcpus, vcpu_index);
> +
> +    vcpu_filename = g_strdup_printf("%s.%u.bb", filename, vcpu_index);
> +    vcpu->file = fopen(vcpu_filename, "w");
> +}
> +
> +static void vcpu_interval_exec(unsigned int vcpu_index, void *udata)
> +{
> +    Vcpu *vcpu = qemu_plugin_scoreboard_find(vcpus, vcpu_index);
> +    GHashTableIter iter;
> +    void *value;
> +
> +    if (!vcpu->file) {
> +        return;
> +    }
> +
> +    vcpu->count -= interval;
> +
> +    fputc('T', vcpu->file);
> +
> +    g_rw_lock_reader_lock(&bbs_lock);
> +    g_hash_table_iter_init(&iter, bbs);
> +
> +    while (g_hash_table_iter_next(&iter, NULL, &value)) {
> +        Bb *bb = value;
> +        uint64_t bb_count = qemu_plugin_u64_get(bb_count_u64(bb), vcpu_index);
> +
> +        if (!bb_count) {
> +            continue;
> +        }
> +
> +        fprintf(vcpu->file, ":%u:%" PRIu64 " ", bb->index, bb_count);
> +        qemu_plugin_u64_set(bb_count_u64(bb), vcpu_index, 0);
> +    }
> +
> +    g_rw_lock_reader_unlock(&bbs_lock);
> +    fputc('\n', vcpu->file);
> +}
> +
> +static void vcpu_tb_trans(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
> +{
> +    uint64_t n_insns = qemu_plugin_tb_n_insns(tb);
> +    uint64_t vaddr = qemu_plugin_tb_vaddr(tb);
> +    Bb *bb;
> +
> +    g_rw_lock_writer_lock(&bbs_lock);
> +    bb = g_hash_table_lookup(bbs, &vaddr);
> +    if (!bb) {
> +        bb = g_new(Bb, 1);
> +        bb->vaddr = vaddr;
> +        bb->count = qemu_plugin_scoreboard_new(sizeof(uint64_t));
> +        bb->index = g_hash_table_size(bbs);
> +        g_hash_table_replace(bbs, &bb->vaddr, bb);
> +    }
> +    g_rw_lock_writer_unlock(&bbs_lock);
> +
> +    qemu_plugin_register_vcpu_tb_exec_inline_per_vcpu(
> +        tb, QEMU_PLUGIN_INLINE_ADD_U64, count_u64(), n_insns);
> +
> +    qemu_plugin_register_vcpu_tb_exec_inline_per_vcpu(
> +        tb, QEMU_PLUGIN_INLINE_ADD_U64, bb_count_u64(bb), n_insns);
> +
> +    qemu_plugin_register_vcpu_tb_exec_cond_cb(
> +        tb, vcpu_interval_exec, QEMU_PLUGIN_CB_NO_REGS,
> +        QEMU_PLUGIN_COND_GE, count_u64(), interval, NULL);
> +}
> +
> +QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
> +                                           const qemu_info_t *info,
> +                                           int argc, char **argv)
> +{
> +    for (int i = 0; i < argc; i++) {
> +        char *opt = argv[i];
> +        g_auto(GStrv) tokens = g_strsplit(opt, "=", 2);
> +        if (g_strcmp0(tokens[0], "interval") == 0) {
> +            interval = g_ascii_strtoull(tokens[1], NULL, 10);
> +        } else if (g_strcmp0(tokens[0], "outfile") == 0) {
> +            filename = tokens[1];
> +            tokens[1] = NULL;
> +        } else {
> +            fprintf(stderr, "option parsing failed: %s\n", opt);
> +            return -1;
> +        }
> +    }
> +
> +    if (!filename) {
> +        fputs("outfile unspecified\n", stderr);
> +        return -1;
> +    }
> +
> +    bbs = g_hash_table_new_full(g_int64_hash, g_int64_equal, NULL, free_bb);
> +    vcpus = qemu_plugin_scoreboard_new(sizeof(Vcpu));
> +    qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
> +    qemu_plugin_register_vcpu_init_cb(id, vcpu_init);
> +    qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans);
> +
> +    return 0;
> +}
> diff --git a/contrib/plugins/Makefile b/contrib/plugins/Makefile
> index edf256cd9d11..6936591b1022 100644
> --- a/contrib/plugins/Makefile
> +++ b/contrib/plugins/Makefile
> @@ -13,6 +13,7 @@ TOP_SRC_PATH = $(SRC_PATH)/../..
>   VPATH += $(SRC_PATH)
>   
>   NAMES :=
> +NAMES += bbv
>   NAMES += execlog
>   NAMES += hotblocks
>   NAMES += hotpages
> 
> ---
> base-commit: 31669121a01a14732f57c49400bc239cf9fd505f
> change-id: 20240618-bb-93387ddf765b
> 
> Best regards,

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>