From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 28D0DC433EF for ; Thu, 14 Oct 2021 08:41:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 05908610EA for ; Thu, 14 Oct 2021 08:41:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230112AbhJNInV (ORCPT ); Thu, 14 Oct 2021 04:43:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:41178 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230042AbhJNInU (ORCPT ); Thu, 14 Oct 2021 04:43:20 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 1338D60F9E; Thu, 14 Oct 2021 08:41:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1634200875; bh=rY9vGtlLDIvkDgY0wX20Oxpih5WsKZMgiPYMwz/VsXE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TsvQCRJ72G2+iekhh/WK3vT5lHlv7ZD6YNQNgAj3L2thXFnBxsGvyUNRW7BamuMqV 1IPExSgJeQI9q0Wym4ATW8HhvO4Aw4CJX4+DsF+KHwMiO6IDjMMu0SjL/bAsfi1hLh r4jkVd+UWyWv+rIV5buFUYY+dM3WYR0t5NCyZNCs= Date: Thu, 14 Oct 2021 10:41:13 +0200 From: Greg KH To: Xianting Tian Cc: jirislaby@kernel.org, amit@kernel.org, arnd@arndb.de, osandov@fb.com, shile.zhang@linux.alibaba.com, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v10 2/3] tty: hvc: pass DMA capable memory to put_chars() Message-ID: References: <20211009114829.1071021-1-xianting.tian@linux.alibaba.com> <20211009114829.1071021-3-xianting.tian@linux.alibaba.com> <3516c58c-e8e6-2e5a-2bc8-ad80e2124d37@linux.alibaba.com> <4dbeddb9-1068-d282-2758-55d0f788ea61@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4dbeddb9-1068-d282-2758-55d0f788ea61@linux.alibaba.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 14, 2021 at 04:34:59PM +0800, Xianting Tian wrote: > > 在 2021/10/10 下午1:33, Greg KH 写道: > > On Sat, Oct 09, 2021 at 11:45:23PM +0800, Xianting Tian wrote: > > > 在 2021/10/9 下午7:58, Greg KH 写道: > > > > Did you look at the placement using pahole as to how this structure now > > > > looks? > > > thanks for all your commnts. for this one, do you mean I need to remove the > > > blank line?  thanks > > > > > No, I mean to use the tool 'pahole' to see the structure layout that you > > just created and determine if it really is the best way to add these new > > fields, especially as you are adding huge buffers with odd alignment. > > thanks, > > Based on your comments, I removed 'char outchar',  remian the position of > 'int outbuf_size' unchanged to keep outbuf_size and lock in the same cache > line.  Now hvc_struct change as below, > >  struct hvc_struct { >         struct tty_port port; >         spinlock_t lock; >         int index; >         int do_wakeup; > -       char *outbuf; >         int outbuf_size; >         int n_outbuf; >         uint32_t vtermno; > @@ -48,6 +57,16 @@ struct hvc_struct { >         struct work_struct tty_resize; >         struct list_head next; >         unsigned long flags; > + > +       /* > +        * the buf is used in hvc console api for putting chars, > +        * and also used in hvc_poll_put_char() for putting single char. > +        */ > +       char cons_outbuf[N_OUTBUF] __ALIGNED__; > +       spinlock_t cons_outbuf_lock; > + > +       /* the buf is used for putting chars to tty */ > +       char outbuf[] __ALIGNED__; >  }; > > pahole for above hvc_struct as below,  is it ok for you?  do we need to pack > the hole? thanks > > struct hvc_struct { >     struct tty_port            port;                 /*     0 352 */ >     /* --- cacheline 5 boundary (320 bytes) was 32 bytes ago --- */ >     spinlock_t                 lock;                 /*   352 4 */ >     int                        index;                /*   356 4 */ >     int                        do_wakeup;            /*   360 4 */ >     int                        outbuf_size;          /*   364 4 */ >     int                        n_outbuf;             /*   368 4 */ >     uint32_t                   vtermno;              /*   372 4 */ >     const struct hv_ops  *     ops;                  /*   376 8 */ >     /* --- cacheline 6 boundary (384 bytes) --- */ >     int                        irq_requested;        /*   384 4 */ >     int                        data;                 /*   388 4 */ >     struct winsize             ws;                   /*   392 8 */ >     struct work_struct         tty_resize;           /*   400 32 */ >     struct list_head           next;                 /*   432 16 */ >     /* --- cacheline 7 boundary (448 bytes) --- */ >     long unsigned int          flags;                /*   448 8 */ > >     /* XXX 56 bytes hole, try to pack */ > >     /* --- cacheline 8 boundary (512 bytes) --- */ >     char                       cons_outbuf[16];      /*   512 16 */ >     spinlock_t                 cons_outbuf_lock;     /*   528 4 */ > >     /* XXX 44 bytes hole, try to pack */ Why not move the spinlock up above the cons_outbuf? Will that not be a bit better? Anyway, this is all fine, and much better than before, thanks. greg k-h