osd: improve hobject_t::to_str() performance

The new version of the code takes only ~70% of the time of the old one.
See https://github.com/ronen-fr/hobjtostr/tree/rf-1 for the code used
to benchmark the performance of this and various other implementations.

Signed-off-by: Ronen Friedman <[email protected]>

Author: ronen-fr

src/common/fmt_common.h

@@ -7,6 +7,7 @@
 /**
  * \file default fmtlib formatters for specifically-tagged types
  */
+#include <fmt/compile.h>
 #include <fmt/format.h>
 
 /**

src/common/hobject.cc

@@ -2,6 +2,8 @@
 // vim: ts=8 sw=2 smarttab
 
 #include <charconv>
+#include <fmt/compile.h>
+#include <fmt/core.h>
 
 #include "hobject.h"
 #include "common/Formatter.h"
@@ -14,23 +16,25 @@ using std::string;
 using ceph::bufferlist;
 using ceph::Formatter;
 
-static void append_escaped(const string &in, string *out)
+namespace {
+void escape_special_chars(const string& in, string* out)
 {
-  for (string::const_iterator i = in.begin(); i != in.end(); ++i) {
-    if (*i == '%') {
+  for (auto c : in) {
+    if (c == '%') {
       out->push_back('%');
       out->push_back('p');
-    } else if (*i == '.') {
+    } else if (c == '.') {
       out->push_back('%');
       out->push_back('e');
-    } else if (*i == '_') {
+    } else if (c == '_') {
       out->push_back('%');
       out->push_back('u');
     } else {
-      out->push_back(*i);
+      out->push_back(c);
     }
   }
 }
+}  // namespace
 
 set<string> hobject_t::get_prefixes(
   uint32_t bits,
@@ -80,33 +84,25 @@ set<string> hobject_t::get_prefixes(
 
 string hobject_t::to_str() const
 {
-  string out;
-
-  char snap_with_hash[1000];
-  char *t = snap_with_hash;
-  const char *end = t + sizeof(snap_with_hash);
-
   uint64_t poolid(pool);
-  t += snprintf(t, end - t, "%.*llX", 16, (long long unsigned)poolid);
-
   uint32_t revhash(get_nibblewise_key_u32());
-  t += snprintf(t, end - t, ".%.*X", 8, revhash);
 
-  if (snap == CEPH_NOSNAP)
-    t += snprintf(t, end - t, ".head");
-  else if (snap == CEPH_SNAPDIR)
-    t += snprintf(t, end - t, ".snapdir");
-  else
-    t += snprintf(t, end - t, ".%llx", (long long unsigned)snap);
-
-  out.append(snap_with_hash, t);
+  string out;
+  if (snap == CEPH_NOSNAP) {
+    out = fmt::format(FMT_COMPILE("{:016X}.{:08X}.head."), poolid, revhash);
+  } else if (snap == CEPH_SNAPDIR) {
+    out = fmt::format(FMT_COMPILE("{:016X}.{:08X}.snapdir."), poolid, revhash);
+  } else {
+    out = fmt::format(
+	FMT_COMPILE("{:016X}.{:08X}.{:X}."), poolid, revhash,
+	(unsigned long long)snap);
+  }
 
+  escape_special_chars(oid.name, &out);
   out.push_back('.');
-  append_escaped(oid.name, &out);
-  out.push_back('.');
-  append_escaped(get_key(), &out);
+  escape_special_chars(get_key(), &out);
   out.push_back('.');
-  append_escaped(nspace, &out);
+  escape_special_chars(nspace, &out);
 
   return out;
 }

src/common/hobject.h

@@ -318,7 +318,7 @@ struct hobject_t {
   void dump(ceph::Formatter *f) const;
   static void generate_test_instances(std::list<hobject_t*>& o);
   friend int cmp(const hobject_t& l, const hobject_t& r);
-  auto operator<=>(const hobject_t &rhs) const noexcept {
+  constexpr auto operator<=>(const hobject_t &rhs) const noexcept {
     auto cmp = max <=> rhs.max;
     if (cmp != 0) return cmp;
     cmp = pool <=> rhs.pool;
@@ -335,7 +335,7 @@ struct hobject_t {
     if (cmp != 0) return cmp;
     return snap <=> rhs.snap;
   }
-  bool operator==(const hobject_t& rhs) const noexcept {
+  constexpr bool operator==(const hobject_t& rhs) const noexcept {
     return operator<=>(rhs) == 0;
   }
   friend struct ghobject_t;
@@ -495,7 +495,7 @@ struct ghobject_t {
   void dump(ceph::Formatter *f) const;
   static void generate_test_instances(std::list<ghobject_t*>& o);
   friend int cmp(const ghobject_t& l, const ghobject_t& r);
-  auto operator<=>(const ghobject_t&) const = default;
+  constexpr auto operator<=>(const ghobject_t&) const = default;
   bool operator==(const ghobject_t&) const = default;
 };
 WRITE_CLASS_ENCODER(ghobject_t)

src/include/object_fmt.h

@@ -5,6 +5,7 @@
 /**
  * \file fmtlib formatters for some object.h structs
  */
+#include <fmt/compile.h>
 #include <fmt/format.h>
 
 #include "object.h"
@@ -24,6 +25,6 @@ struct fmt::formatter<snapid_t> {
     if (snp == CEPH_SNAPDIR) {
       return fmt::format_to(ctx.out(), "snapdir");
     }
-    return fmt::format_to(ctx.out(), "{:x}", snp.val);
+    return fmt::format_to(ctx.out(), FMT_COMPILE("{:x}"), snp.val);
   }
 };

src/include/types.h

@@ -513,7 +513,7 @@ struct shard_id_t {
   shard_id_t() : id(0) {}
   constexpr explicit shard_id_t(int8_t _id) : id(_id) {}
 
-  operator int8_t() const { return id; }
+  constexpr operator int8_t() const { return id; }
 
   const static shard_id_t NO_SHARD;