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Re: [Qemu-devel] [PATCH v7 07/42] ram_debug_dump_bitmap: Dump a migratio
From: |
Juan Quintela |
Subject: |
Re: [Qemu-devel] [PATCH v7 07/42] ram_debug_dump_bitmap: Dump a migration bitmap as text |
Date: |
Mon, 13 Jul 2015 12:15:34 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
"Dr. David Alan Gilbert" <address@hidden> wrote:
> * Juan Quintela (address@hidden) wrote:
>> "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?
>
> 'migration_bitmap' is static to ram.c, so allowing NULL to get
> you a dump of the migration_bitmap means that if you call this
> dump routine from any error path you're debugging anywhere in qemu
> then you can dump the migration bitmap. e.g. I was adding calls
> to this in migration.c and migration/postcopy-ram.c in error
> paths I was trying to debug.
ok.
>
>> > + 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?
>
> It's easier to see an occasional '1' in a big field of .'s.
ok.
>
>> > + 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?
>
> Here's a compile-tested-only version using find_ - it's bigger, if you think
> it's better I can use this instead:
>
> 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;
>
> if (!todump) {
> todump = migration_bitmap;
> }
>
> for (cur = 0; cur < ram_pages; cur += linelen) {
> int64_t curb;
> unsigned long next_bit;
>
> /*
> * Last line; catch the case where the line length
> * is longer than remaining ram
> */
> if (cur + linelen > ram_pages) {
> linelen = ram_pages - cur;
> }
> if (expected) {
> next_bit = find_next_bit(todump, cur + linelen, cur);
> } else {
> next_bit = find_next_zero_bit(todump, cur + linelen, cur);
> }
> if (next_bit >= (cur + linelen)) {
> continue;
> }
>
> for (curb = 0; curb < linelen; curb++) {
> bool thisbit = test_bit(cur + curb, todump);
> fputc(thisbit ? '1' : '.', stderr);
> }
> fputc('\n', stderr);
> }
> }
>
> Dave
Reviewed-by: Juan Quintela <address@hidden>
>
>
>>
>> Later, Juan.
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
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