Improve ioctx wait diagnostic message

src/fellow_log.c

@@ -592,6 +592,8 @@ fellow_io_ring_size(const char *envvar)
 struct fellow_fd_ioctx {
 	unsigned			magic;
 #define FELLOW_FD_IOCTX_MAGIC		0x3b19f0e1
+	unsigned			waits;
+	vtim_mono			waits_t0;
 	struct bitf			bitf[1];
 	char				_spc[bitf_sz1(FELLOW_NIOCTX) -
 					     sizeof(struct bitf)];
@@ -725,6 +727,8 @@ static void
 fellow_fd_ioctx_get(struct fellow_fd *ffd, struct fellow_fd_ioctx_lease *fdil)
 {
 	struct fellow_fd_ioctx *fdio;
+	unsigned waits = 0;
+	vtim_dur waits_d = -1;	// flint
 	size_t f;
 
 	CHECK_OBJ_NOTNULL(ffd, FELLOW_FD_MAGIC);
@@ -742,18 +746,34 @@ fellow_fd_ioctx_get(struct fellow_fd *ffd, struct fellow_fd_ioctx_lease *fdil)
 		/* this should never happen, but if it does,
 		 * we do not want it to be fatal
 		 */
-		ffd->diag("WARN: ioctx wait\n");
+		if (fdio->waits > 0)
+			fdio->waits++;
+		else {
+			fdio->waits = 1;
+			fdio->waits_t0 = VTIM_mono();
+		}
 		AZ(pthread_cond_wait(&fdio->cond, &fdio->mtx));
 		f = bitf_ffs(fdio->bitf);
 	}
 	AN(f);
 	f--;
 	AN(bitf_clr(fdio->bitf, f));
+	if (fdio->waits > 0 &&
+	    (waits_d = VTIM_mono() - fdio->waits_t0) > 1.0) {
+		waits = fdio->waits;
+		fdio->waits = 0;
+		fdio->waits_t0 = 0;
+	}
 	AZ(pthread_mutex_unlock(&fdio->mtx));
 
 	fdil->fdio = fdio;
 	fdil->ioctxp = &fdio->ioctx[f];
 	TAKEZN(fdil->ioctx, *fdil->ioctxp);
+
+	if (waits) {
+		ffd->diag("WARN: %u ioctx waits in %.2fs (%.2f/s)",
+		    waits, waits_d, (double)waits / waits_d);
+	}
 }
 
 static void