Re: [Qemu-devel] [PATCH v7 07/42] ram_debug_dump_bitmap: Dump a migration bitmap as text

[Juan Quintela]

"Dr. David Alan Gilbert (git)" <address@hidden> wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
>
> Useful for debugging the migration bitmap and other bitmaps
> of the same format (including the sentmap in postcopy).
>
> The bitmap is printed to stderr.
> Lines that are all the expected value are excluded so the output
> can be quite compact for many bitmaps.
>
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> ---
>  include/migration/migration.h |  1 +
>  migration/ram.c               | 38 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 39 insertions(+)
>
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index 9387c8c..b3a7f75 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -144,6 +144,7 @@ uint64_t xbzrle_mig_pages_cache_miss(void);
>  double xbzrle_mig_cache_miss_rate(void);
>  
>  void ram_handle_compressed(void *host, uint8_t ch, uint64_t size);
> +void ram_debug_dump_bitmap(unsigned long *todump, bool expected);
>  
>  /**
>   * @migrate_add_blocker - prevent migration from proceeding
> diff --git a/migration/ram.c b/migration/ram.c
> index 57368e1..efc215a 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1051,6 +1051,44 @@ static void reset_ram_globals(void)
>  
>  #define MAX_WAIT 50 /* ms, half buffered_file limit */
>  
> +/*
> + * 'expected' is the value you expect the bitmap mostly to be full
> + * of; it won't bother printing lines that are all this value.
> + * If 'todump' is null the migration bitmap is dumped.
> + */
> +void ram_debug_dump_bitmap(unsigned long *todump, bool expected)
> +{
> +    int64_t ram_pages = last_ram_offset() >> TARGET_PAGE_BITS;
> +
> +    int64_t cur;
> +    int64_t linelen = 128;
> +    char linebuf[129];
> +
> +    if (!todump) {
> +        todump = migration_bitmap;
> +    }

Why?  Just alssert that todump!= NULL?


> +
> +    for (cur = 0; cur < ram_pages; cur += linelen) {
> +        int64_t curb;
> +        bool found = false;
> +        /*
> +         * Last line; catch the case where the line length
> +         * is longer than remaining ram
> +         */
> +        if (cur + linelen > ram_pages) {
> +            linelen = ram_pages - cur;
> +        }
> +        for (curb = 0; curb < linelen; curb++) {
> +            bool thisbit = test_bit(cur + curb, todump);
> +            linebuf[curb] = thisbit ? '1' : '.';

Put 1 and 0?  Why the dot?

> +            found = found || (thisbit != expected);
> +        }
> +        if (found) {
> +            linebuf[curb] = '\0';
> +            fprintf(stderr,  "0x%08" PRIx64 " : %s\n", cur, linebuf);
> +        }
> +    }
> +}


And once here, why are we doing it this way?  We have

find_first_bit(addr, nbits) and find_first_zero_bit(addr, nbits) and
friends?

Doiwg the walk by hand looks weird, no?

Later, Juan.