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Tue, 27 Oct 2026 20:22:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793132548; bh=CumA5wja+462jEhi0a3U0wA6ylj10YfDNF6b/OlvitE=; h=From:Date:Subject:References:In-Reply-To:To:Cc:Reply-To; b=AkOkJj1c7Ey9wifQItVmmXN8+F9FG5snzrAc0J0rh5PVOu6zJVY9fsIeg4c/P/vPJ PsuGJOLVYUc6W7adm37lCmLM/DAiywTkb5rIN0qSVj81bjAXWqLpn4t62+y5pOfBO8 UdevwrFWeIHujsK6hxPnwcSGeuNL+UODWxp+7/XjrxDhRayuRhPUZCt85mcmuFYgA6 llpTloSfPQVLt6/kUcg2MuwptWMHWUSu1bVPm+gxZzrk/fthuf7oqmgrhXNziCCcdw nbkvmIamUZGYIZF8GVgOb4CiEAAoUW5uT5VG5d+2+t4vuRdnCTnUNfB5zUrKGXxMOH biFcM5wNVncAQ== Received: from nexus.subspace.kernel.org (localhost [IPv6:::1]) by lkml.kernel.org (Postfix) with ESMTP id 76FF24528C; Tue, 27 Oct 2026 20:22:11 +0000 (UTC) From: Jim Cromie via B4 Relay Date: Tue, 27 Oct 2026 14:22:39 -0600 Subject: [PATCH v13 39/39] drm: Mark __drm_debug as __read_mostly X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Message-Id: <20261027-dd-cmap-part2-clean-v13-39-9267923be612@gmail.com> References: <20261027-dd-cmap-part2-clean-v13-0-9267923be612@gmail.com> In-Reply-To: <20261027-dd-cmap-part2-clean-v13-0-9267923be612@gmail.com> To: Jason Baron , Shuah Khan , Andrew Morton , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Arnd Bergmann , Luis Chamberlain , Petr Pavlu , Daniel Gomez , Sami Tolvanen , Aaron Tomlin , Jonathan Corbet , Greg Kroah-Hartman , Nathan Chancellor , Nicolas Schier , Shuah Khan , Randy Dunlap , "Rafael J. Wysocki" , Pavel Machek , Len Brown , Jonathan Corbet , Petr Mladek , Steven Rostedt , John Ogness , Sergey Senozhatsky , =?utf-8?q?Thomas_Wei=C3=9Fschuh?= , "Jason A. Donenfeld" Cc: linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-arch@vger.kernel.org, linux-modules@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-pm@vger.kernel.org, Jason Baron , Jim Cromie X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1793132527; l=1613; i=jim.cromie@gmail.com; s=20260203; h=from:subject:message-id; bh=t+nRtOhFy0vKw6kQ27p3cuieeS36YDxQ0XXNRXZWkUg=; b=f5HxtzzpGBAtoIjrGk99drDPUwR9c509I4kbOa/UvLUvVSU/1Ym+S3Zc4ZQq7x1BvvmPGB9Rm Y0okPVIzszEA9IDtp+xPo+JJyW8Kn7/HOaJh88Ct0eGqz1QL/OnW11t X-Developer-Key: i=jim.cromie@gmail.com; a=ed25519; pk=C6E5ODlPQo7ZBynATXH9wg7K6HxP0pIXyf4s38Qw0XE= X-Endpoint-Received: by B4 Relay for jim.cromie@gmail.com/20260203 with auth_id=958 X-Original-From: Jim Cromie Reply-To: jim.cromie@gmail.com Content-Transfer-Encoding: 7bit From: Jim Cromie Dyndbg classmaps converts ~5,700 DRM debug callsites into static keys, yielding 0-off-cost NOOPs that never touch memory. However, several call patterns do not fit the direct drm_dbg() macro model; notably open-coded drm_debug_enabled() guard blocks, drm_dbg_printer(), and ratelimited helpers. In upstream, the linker places __drm_debug in the same 64-byte cacheline as hot writers: drm_lease_idr_object, drm_global_mutex. Writes to those locks issue Request-For-Ownership (RFO) invalidations across cores, leaving those residual bit-tests to suffer 7 false-sharing hazards and continuous cache bouncing during active rendering (e.g. 12 concurrent vkcube clients). In contrast, writes to __drm_debug occur almost never, only when userspace updates "/sys/module/drm/parameters/debug". So mark __drm_debug with __read_mostly. This isolates it from the 7 writable symbols it currently shares a cache-line with, eliminating those invalidations. Signed-off-by: Jim Cromie --- drivers/gpu/drm/drm_print.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c index 794417c62097..1ec139c8f06f 100644 --- a/drivers/gpu/drm/drm_print.c +++ b/drivers/gpu/drm/drm_print.c @@ -40,7 +40,7 @@ * __drm_debug: Enable debug output. * Bitmask of DRM_UT_x. See include/drm/drm_print.h for details. */ -u32 __drm_debug; +u32 __drm_debug __read_mostly; EXPORT_SYMBOL(__drm_debug); MODULE_PARM_DESC(debug, "Enable debug output, where each bit enables a debug category.\n" -- 2.56.0