From nobody Sat Feb 7 07:26:00 2026 Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5FC1722D7B1; Fri, 23 Jan 2026 15:53:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.13 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769183632; cv=none; b=GHbNaUO5XYTTe1gDvx1WB5yx/mgkXPZSycP1JEkQgEu153cAyDFXg8rBrxdhToLLML79MOkMklJgjYvCuBx218cuHzWpvydXm1a+zvv73PflTEYlP4nqoSncojtd9eThBt76+ZZgHgHv/X8afR5Vsz1J2XRzRRfjoyuhZbg/KGI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769183632; c=relaxed/simple; bh=WIcz4SEjB3JTdLfmWpv8/EmdIZIDGm9Lagq/NT5yDBI=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type; b=qSZBJH5du8Zl8cX3Xj8ypBJKwlZL58kwFT/1ZBkcnDHVtSLj+onYxvAKtZt0r9LMOdsUDPmyD9N1yDqj5sk9nGQagOfBgJOW2euN6vPUdsSae0uO6LicT61hwm2xIdUcC5qCsQUi4z97Uh8RjVtxz/0cpq6wq9nNbqfJxgr7Tso= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.13 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 28FC78B749; Fri, 23 Jan 2026 15:53:49 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf06.hostedemail.com (Postfix) with ESMTPA id 7F5B920010; Fri, 23 Jan 2026 15:53:47 +0000 (UTC) Date: Fri, 23 Jan 2026 10:54:15 -0500 From: Steven Rostedt To: LKML , Linux Trace Kernel Cc: Masami Hiramatsu , Mathieu Desnoyers , Tom Zanussi Subject: [PATCH] tracing: Up the hist stacktrace size from 16 to 31 Message-ID: <20260123105415.2be26bf4@gandalf.local.home> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Stat-Signature: x861r98ybrt3gjui4f4afx3ne6s115be X-Rspamd-Server: rspamout03 X-Rspamd-Queue-Id: 7F5B920010 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX19vqqBjOjrK7k9mi9j+cH+US+K5a+4H06M= X-HE-Tag: 1769183627-766583 X-HE-Meta: U2FsdGVkX19LeirWW+Jix0+0TPV+FQNplR3TP69h2XCEjb9dbt8y0lo9t/qGB7gn93ay34DlS2KbFIXr3F/krQ8ImjWI6kAeU/8uBPMmyKFV83K5Y9Tpa25mtHhIM0xa3/wVV2+a4wSgVoy3VbZ2fsbQYyfSfDlyd4PsIwq5JwPbi/dm94wul1TTHZZBsRD6S6S2icP/IkzD3EFE0oae9Bshf8YFWSU7h5r38UBxyx7rVnSocK9CGP/rrXM0Oa8N0pNIdnd/QLuA8SEg2N2tkG2u81/bIwYRs18wWuBJNoRdhUw1FyYZQO8totdA8U35CT5jqhndfOuFneDm4hOyekDzJwFtmAwvL6lPfHHOJSXksIbaQmZoqoCy6hybmsUp Content-Type: text/plain; charset="utf-8" From: Steven Rostedt Recording stacktraces is very useful, but the size of 16 deep is very restrictive. For example, in seeing where tasks schedule out in a non running state, the following can be used: ~# cd /sys/kernel/tracing ~# echo 'hist:keys=3Dcommon_stacktrace:vals=3Dhitcount if prev_state & 3' = > events/sched/sched_switch/trigger ~# cat events/sched/sched_switch/hist [..] { common_stacktrace: __schedule+0xdc0/0x1860 schedule+0x27/0xd0 schedule_timeout+0xb5/0x100 wait_for_completion+0x8a/0x140 xfs_buf_iowait+0x20/0xd0 [xfs] xfs_buf_read_map+0x103/0x250 [xfs] xfs_trans_read_buf_map+0x161/0x310 [xfs] xfs_btree_read_buf_block+0xa0/0x120 [xfs] xfs_btree_lookup_get_block+0xa3/0x1e0 [xfs] xfs_btree_lookup+0xea/0x530 [xfs] xfs_alloc_fixup_trees+0x72/0x570 [xfs] xfs_alloc_ag_vextent_size+0x67f/0x800 [xfs] xfs_alloc_vextent_iterate_ags.constprop.0+0x52/0x230 [xfs] xfs_alloc_vextent_start_ag+0x9d/0x1b0 [xfs] xfs_bmap_btalloc+0x2af/0x680 [xfs] xfs_bmapi_allocate+0xdb/0x2c0 [xfs] } hitcount: 1 [..] The above stops at 16 functions where knowing more would be useful. As the allocated storage for stacks is the same for strings, and that size is 256 bytes, there is a lot of space not being used for stacktraces. 16 * 8 =3D 128 Up the size to 31 (it requires the last slot to be zero, so it can't be 32). Also change the BUILD_BUG_ON() to allow the size of the stacktrace storage to be equal to the max size. It already accounts for the empty slot via a "+ 1": BUILD_BUG_ON((HIST_STACKTRACE_DEPTH + 1) * sizeof(long) >=3D STR_VAR_LEN_= MAX); Change that from ">=3D" to just ">", as now they are equal. Signed-off-by: Steven Rostedt (Google) Reviewed-by: Tom Zanussi --- kernel/trace/trace.h | 2 +- kernel/trace/trace_events_hist.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 8888fc9335b6..69e7defba6c6 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -128,7 +128,7 @@ enum trace_type { =20 #define FAULT_STRING "(fault)" =20 -#define HIST_STACKTRACE_DEPTH 16 +#define HIST_STACKTRACE_DEPTH 31 #define HIST_STACKTRACE_SIZE (HIST_STACKTRACE_DEPTH * sizeof(unsigned long= )) #define HIST_STACKTRACE_SKIP 5 =20 diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_h= ist.c index 24441b30a1a4..dfb7c4754bf8 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -3154,7 +3154,7 @@ static inline void __update_field_vars(struct tracing= _map_elt *elt, u64 var_val; =20 /* Make sure stacktrace can fit in the string variable length */ - BUILD_BUG_ON((HIST_STACKTRACE_DEPTH + 1) * sizeof(long) >=3D STR_VAR_LEN_= MAX); + BUILD_BUG_ON((HIST_STACKTRACE_DEPTH + 1) * sizeof(long) > STR_VAR_LEN_MAX= ); =20 for (i =3D 0, j =3D field_var_str_start; i < n_field_vars; i++) { struct field_var *field_var =3D field_vars[i]; --=20 2.51.0