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From: "Ma, WenwuX" <wenwux.ma@intel.com>
To: Thomas Monjalon <thomas@monjalon.net>,
	"fengchengwen@huawei.com" <fengchengwen@huawei.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
	"Jiale, SongX" <songx.jiale@intel.com>,
	"stable@dpdk.org" <stable@dpdk.org>
Subject: RE: [PATCH v3] dmadev: fix structure alignment
Date: Thu, 21 Mar 2024 09:18:21 +0000	[thread overview]
Message-ID: <MN0PR11MB61108C052D9508FCD5092EA2EB322@MN0PR11MB6110.namprd11.prod.outlook.com> (raw)
In-Reply-To: <2631241.9Mp67QZiUf@thomas>

Hi, Thomas

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Thursday, March 21, 2024 4:31 PM
> To: fengchengwen@huawei.com; Ma, WenwuX <wenwux.ma@intel.com>
> Cc: dev@dpdk.org; Jiale, SongX <songx.jiale@intel.com>; stable@dpdk.org
> Subject: Re: [PATCH v3] dmadev: fix structure alignment
> 
> 21/03/2024 02:25, Ma, WenwuX:
> > Hi, Thomas
> >
> > From: Thomas Monjalon <thomas@monjalon.net>
> > > 20/03/2024 08:23, Wenwu Ma:
> > > > The structure rte_dma_dev needs to be aligned to the cache line,
> > > > but the return value of malloc may not be aligned to the cache
> > > > line. When we use memset to clear the rte_dma_dev object, it may
> > > > cause a segmentation fault in clang-x86-platform.
> > > >
> > > > This is because clang uses the "vmovaps" assembly instruction for
> > > > memset, which requires that the operands (rte_dma_dev objects)
> > > > must aligned on a 16-byte boundary or a general-protection
> > > > exception (#GP) is generated.
> > > >
> > > > Therefore, either additional memory is applied for re-alignment,
> > > > or the rte_dma_dev object does not require cache line alignment.
> > > > The patch chooses the former option to fix the issue.
> > > >
> > > > Fixes: b36970f2e13e ("dmadev: introduce DMA device library")
> > > > Cc: stable@dpdk.org
> > > >
> > > > Signed-off-by: Wenwu Ma <wenwux.ma@intel.com>
> > > [..]
> > > > -	size = dma_devices_max * sizeof(struct rte_dma_dev);
> > > > -	rte_dma_devices = malloc(size);
> > > > -	if (rte_dma_devices == NULL)
> > > > +	/* The dma device object is expected to align cacheline, but
> > > > +	 * the return value of malloc may not be aligned to the cache line.
> > > > +	 * Therefore, extra memory is applied for realignment.
> > > > +	 * note: We do not call posix_memalign/aligned_alloc because it is
> > > > +	 * version dependent on libc.
> > > > +	 */
> > > > +	size = dma_devices_max * sizeof(struct rte_dma_dev) +
> > > > +		RTE_CACHE_LINE_SIZE;
> > > > +	ptr = malloc(size);
> > > > +	if (ptr == NULL)
> > > >  		return -ENOMEM;
> > > > -	memset(rte_dma_devices, 0, size);
> > > > +	memset(ptr, 0, size);
> > > > +
> > > > +	rte_dma_devices = RTE_PTR_ALIGN(ptr, RTE_CACHE_LINE_SIZE);
> > >
> > > Why not using aligned_alloc()?
> > > https://en.cppreference.com/w/c/memory/aligned_alloc
> > >
> > >
> > because it is version dependent on libc.
> 
> Which libc is required?
> 

using the 'man aligned_alloc' command, we has the following description:

VERSIONS
       The functions memalign(), valloc(), and pvalloc() have been available in all Linux libc libraries.

       The function aligned_alloc() was added to glibc in version 2.16.

       The function posix_memalign() is available since glibc 2.1.91.


  parent reply	other threads:[~2024-03-21  9:18 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-03-08  5:37 [PATCH] " Wenwu Ma
2024-03-08  7:01 ` fengchengwen
2024-03-15  1:43 ` [PATCH v2] " Wenwu Ma
2024-03-15  6:02   ` Tyler Retzlaff
2024-03-15  6:06   ` fengchengwen
2024-03-15  6:25     ` Ma, WenwuX
2024-03-15  7:44       ` Ma, WenwuX
2024-03-15  8:31         ` fengchengwen
2024-03-15  9:27           ` Ma, WenwuX
2024-03-20  4:11             ` fengchengwen
2024-03-20  7:34               ` Ma, WenwuX
2024-03-19  9:48   ` Jiale, SongX
2024-03-20  7:23 ` [PATCH v3] " Wenwu Ma
2024-03-20  9:31   ` fengchengwen
2024-06-27 12:46     ` Thomas Monjalon
2024-03-20 11:37   ` Thomas Monjalon
2024-03-21  1:25     ` Ma, WenwuX
2024-03-21  8:30       ` Thomas Monjalon
2024-03-21  8:57         ` Ma, WenwuX
2024-03-21  9:18         ` Ma, WenwuX [this message]
2024-03-21 10:06           ` Thomas Monjalon
2024-03-21 16:05             ` Tyler Retzlaff

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