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X-IronPort-AV: E=McAfee;i="6600,9927,10949"; a="465067557" X-IronPort-AV: E=Sophos;i="6.04,184,1695711600"; d="scan'208";a="465067557" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Jan 2024 15:01:37 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10949"; a="925799297" X-IronPort-AV: E=Sophos;i="6.04,184,1695711600"; d="scan'208";a="925799297" Received: from tassilo.jf.intel.com (HELO tassilo.localdomain) ([10.54.38.190]) by fmsmga001.fm.intel.com with ESMTP; 10 Jan 2024 15:01:36 -0800 Received: by tassilo.localdomain (Postfix, from userid 1000) id 2636F301C53; Wed, 10 Jan 2024 15:01:36 -0800 (PST) From: Andi Kleen To: Oscar Salvador Cc: andrey.konovalov@linux.dev, Andrew Morton , Andrey Konovalov , Marco Elver , Alexander Potapenko , Dmitry Vyukov , Vlastimil Babka , kasan-dev@googlegroups.com, Evgenii Stepanov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrey Konovalov Subject: Re: [PATCH v4 12/22] lib/stackdepot: use read/write lock In-Reply-To: (Oscar Salvador's message of "Wed, 3 Jan 2024 10:14:42 +0100") References: <9f81ffcc4bb422ebb6326a65a770bf1918634cbb.1700502145.git.andreyknvl@google.com> Date: Wed, 10 Jan 2024 15:01:36 -0800 Message-ID: <87sf34lrn3.fsf@linux.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Rspam-User: X-Stat-Signature: ic13wndpn1uhbs65uze6yjhg67sozrwe X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 050D920017 X-HE-Tag: 1704927698-217661 X-HE-Meta: U2FsdGVkX1/ofdy2SUFFKfilFkJzEZQnns3tsHCwDBlSlEZ43RnlGnOnQCWMkkFCgAT25PulARgn1exi9XlKTEOt/DVWmzK6dySBT1oX9dBFkNN/h7BhIz6K6/tE6C9AJYmwnmni+ebvl2WVhJ2iMPYHwhQ/S3oFQa9p0yk3y+WS2xu87+KN5j7ZikxL/JWyJbmYIClCHrKqCHtGZfEiJuYjy1Xersj0sveJzK+lyIy/BLSXdQrEp+z0DiG6KxooAsPGujV+hXQ27I7/1j8COlYQ6MLwPajPfnU2q+/U2jrQ2bESJFm/zEmH8ZIndhkCUL5FFmRF6Vh0EE1GB4llljwksjEMbCGUmT1B1NtAdd0pbGF/BpQkgd4JdtZyB/5oIFrPluL1gJySSNrE7u7seMMTLg0xZZ6NkNb8SMTjL56eF4UzkIUruKTFPr8H6SVzqtMrcuiNEJBtKFk0xTBAqEajsG3ylo3t5qUdUUWWne4xTwdI3rptowIREQlcOd2s3jgEO0mVueaZVHtKh2N/FK4IPVFexAs6T0TBSra0blPtCDvBjfML5vtXvYtYjoDB5ALjImesmu7rD97Z3h1bVDvputfd+ZxCQLUizoF2f8dBGA9wj2o47y29p14KstOLmHSihk4cmaORBOFRBwU2QhpiEJmDToj4/GHk0lW+xX95nABHy2BE00IMHf/zjpsjdRc8znNUR6V6eIsiZ8nN/0KcroBLYbV880QoMWhJE2Ki7/QZwnFRo3N46rSf3PipF3iZAaB1mxP8QzFlDyWFeVNFUhy63IncWXKc710J94Kjq9sBue0jSPVTpsXlWEvydKr8p6CcAz+RKMvI3bpFCokNfJPkyc8d0lX3Ktq1GhNJBRhaWBKC6n/5psTu2RMbI/Fk0wjtDkuWavgC3D+MgEIxFFmB2Iy18HKONroy+TWi7r9sEbxV4Hf3q1F/yH6lziOfovYX8EoUoq2zvzi 5AVLamu7 zT/1RSP8vL4A8lPE/jjhmPANDoRnMCAtRKODPRHEz2kkMFgAVicYPzt6NzrGr60x7hHP53u051yzUBy+OTOOi5ALwLGweU4e0qRWkzifDGfYUi80jSyI2zoEyPot1Ao0CY6pbsgN6sUnNq3k= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Oscar Salvador writes: >> >> With this change, multiple users can still look up records in parallel. That's a severe misunderstanding -- rwlocks always bounce a cache line, so the parallelism is significantly reduced. Normally rwlocks are only worth it if your critical region is quite long. >> >> This is preparatory patch for implementing the eviction of stack records >> from the stack depot. >> >> Reviewed-by: Alexander Potapenko >> Signed-off-by: Andrey Konovalov > > Reviewed-by: Oscar Salvador Has anyone benchmarked this on a high core count machine? It sounds pretty bad if every lock aquisition starts bouncing a single cache line. Consider using RCU or similar. -Andi