Re: [RFC PATCH v2 2/3] plugins: cache: Enabled parameterization and added trace printing

[Mahmoud Mandour <ma.mandourr@gmail.com>]

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On Tue, Jun 1, 2021 at 1:29 PM Alex Bennée <alex.bennee@linaro.org> wrote:

>
> (Stefan CC'ed for tracing discussion)
>
> Mahmoud Mandour <ma.mandourr@gmail.com> writes:
>
> > Made both icache and dcache configurable through plugin arguments
> > and added memory trace printing in a separate file.
>
> Please keep the commits discreet and single topic. The memory trace is
> an extra feature so should be in it's own commit.
>
> >
> > Signed-off-by: Mahmoud Mandour <ma.mandourr@gmail.com>
> > ---
> >  contrib/plugins/cache.c | 68 +++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 66 insertions(+), 2 deletions(-)
> >
> > diff --git a/contrib/plugins/cache.c b/contrib/plugins/cache.c
> > index 8c9d1dd538..fa0bf1dd40 100644
> > --- a/contrib/plugins/cache.c
> > +++ b/contrib/plugins/cache.c
> > @@ -22,7 +22,7 @@ static GRand *rng;
> >  static GHashTable *dmiss_ht;
> >  static GHashTable *imiss_ht;
> >
> > -static GMutex dmtx, imtx;
> > +static GMutex dmtx, imtx, fmtx;
> >
> >  static int limit;
> >  static bool sys;
> > @@ -33,6 +33,8 @@ static uint64_t dmisses;
> >  static uint64_t imem_accesses;
> >  static uint64_t imisses;
> >
> > +FILE *tracefile;
> > +
> >  static enum qemu_plugin_mem_rw rw = QEMU_PLUGIN_MEM_RW;
> >
> >  enum AccessResult {
> > @@ -205,6 +207,16 @@ static void vcpu_mem_access(unsigned int cpu_index,
> qemu_plugin_meminfo_t info,
> >      insn_addr = ((struct InsnData *) userdata)->addr;
> >      effective_addr = hwaddr ? qemu_plugin_hwaddr_phys_addr(hwaddr) :
> vaddr;
> >
> > +    if (tracefile) {
> > +        g_mutex_lock(&fmtx);
> > +        g_autoptr(GString) rep = g_string_new("");
> > +        bool is_store = qemu_plugin_mem_is_store(info);
> > +        g_string_append_printf(rep, "%c: 0x%" PRIx64,
> > +                is_store ? 'S' : 'L', effective_addr);
> > +        fprintf(tracefile, "%s\n", rep->str);
> > +        g_mutex_unlock(&fmtx);
> > +    }
>
> I can see this would be useful for debugging but I'm wary of adding
> ad-hoc tracing formats when QEMU already has support for a wide range of
> tracing formats. We discussed this a bit in:
>
>   Subject: trace_FOO_tcg bit-rotted?
>   Date: Tue, 06 Apr 2021 17:00:20 +0100
>   Message-ID: <87eefnwd0l.fsf@linaro.org>
>
> However I don't know how easy it would be to leverage the existing
> tracing infrastructure from inside a plugin. As I understand it QEMU
> currently builds a static list of trace points during the build so maybe
> we would need additional infrastructure for a plugin to register a trace
> point and for the final output to be use-able. For example the binary
> trace output I think still needs to reference the source trace-events
> file?
>
> So that's not a NACK but maybe we could spend a little time working out
> if we can come up with a cleaner solution?

Alright then, I will have it removed for now and maybe add it if there's a
better
solution for it.

>


> Stefan, any thoughts?
>
> >      if (access_cache(dcache, effective_addr) == MISS) {
> >          struct InsnData *insn = get_or_create(dmiss_ht, userdata,
> insn_addr);
> >          insn->misses++;
> > @@ -221,11 +233,20 @@ static void vcpu_insn_exec(unsigned int
> vcpu_index, void *userdata)
> >      g_mutex_lock(&imtx);
> >      addr = ((struct InsnData *) userdata)->addr;
> >
> > +    if (tracefile) {
> > +        g_mutex_lock(&fmtx);
> > +        g_autoptr(GString) rep = g_string_new("");
> > +        g_string_append_printf(rep, "I: 0x%" PRIx64, addr);
> > +        fprintf(tracefile, "%s\n", rep->str);
> > +        g_mutex_unlock(&fmtx);
> > +    }
> > +
> >      if (access_cache(icache, addr) == MISS) {
> >          struct InsnData *insn = get_or_create(imiss_ht, userdata, addr);
> >          insn->misses++;
> >          imisses++;
> >      }
> > +
> >      imem_accesses++;
> >      g_mutex_unlock(&imtx);
> >  }
> > @@ -352,6 +373,15 @@ static void plugin_exit()
> >
> >      g_mutex_unlock(&dmtx);
> >      g_mutex_unlock(&imtx);
> > +
> > +    if (tracefile) {
> > +        fclose(tracefile);
> > +    }
> > +}
> > +
> > +static bool bad_cache_params(int blksize, int assoc, int cachesize)
> > +{
> > +    return (cachesize % blksize) != 0 || (cachesize % (blksize * assoc)
> != 0);
> >  }
> >
> >  QEMU_PLUGIN_EXPORT
> > @@ -377,14 +407,48 @@ int qemu_plugin_install(qemu_plugin_id_t id, const
> qemu_info_t *info,
> >
> >      for (i = 0; i < argc; i++) {
> >          char *opt = argv[i];
> > -        if (g_str_has_prefix(opt, "limit=")) {
> > +        if (g_str_has_prefix(opt, "I=")) {
> > +            gchar **toks = g_strsplit(opt + 2, " ", -1);
> > +            if (g_strv_length(toks) != 3) {
> > +                fprintf(stderr, "option parsing failed: %s\n", opt);
> > +                return -1;
> > +            }
> > +            icachesize = g_ascii_strtoull(toks[0], NULL, 10);
> > +            iassoc = g_ascii_strtoull(toks[1], NULL, 10);
> > +            iblksize = g_ascii_strtoull(toks[2], NULL, 10);
> > +        } else if (g_str_has_prefix(opt, "D=")) {
> > +            gchar **toks = g_strsplit(opt + 2, " ", -1);
> > +            if (g_strv_length(toks) != 3) {
> > +                fprintf(stderr, "option parsing failed: %s\n", opt);
> > +                return -1;
> > +            }
> > +            dcachesize = g_ascii_strtoull(toks[0], NULL, 10);
> > +            dassoc = g_ascii_strtoull(toks[1], NULL, 10);
> > +            dblksize = g_ascii_strtoull(toks[2], NULL, 10);
> > +        } else if (g_str_has_prefix(opt, "limit=")) {
> >              limit = g_ascii_strtoull(opt + 6, NULL, 10);
> > +        } else if (g_str_has_prefix(opt, "tracefile=")) {
> > +            char *file_name = opt + 10;
> > +            tracefile = fopen(file_name, "w");
> > +            if (!tracefile) {
> > +                fprintf(stderr, "could not open: %s for writing\n",
> file_name);
> > +            }
> >          } else {
> >              fprintf(stderr, "option parsing failed: %s\n", opt);
> >              return -1;
> >          }
> >      }
> >
> > +    if (bad_cache_params(iblksize, iassoc, icachesize)) {
> > +        fprintf(stderr, "icache cannot be constructed from given
> parameters\n");
> > +        return -1;
> > +    }
> > +
> > +    if (bad_cache_params(dblksize, dassoc, dcachesize)) {
> > +        fprintf(stderr, "dcache cannot be constructed from given
> parameters\n");
> > +        return -1;
> > +    }
> > +
>
> Perhaps roll bad_cache_params into cache_init and return NULL if it
> fails, so:
>
>   dcache = cache_init(dblksize, dassoc, dcachesize);
>   if (!dcache) {
>     fprintf(stderr, "dcache cannot be constructed from given
> parameters\n");
>     return -1;
>   }

Applied, thanks

>
> >      dcache = cache_init(dblksize, dassoc, dcachesize);
> >      icache = cache_init(iblksize, iassoc, icachesize);
>
>
> --
> Alex Bennée
>

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