From: Imran Khan <kimran@codeaurora.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: "\"Chalamarla," "Tirumalesh\""
"<Tirumalesh.Chalamarla@caviumnetworks.com>;Ganesh" Mahendran
<opensource.ganesh@gmail.com>,
"open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] Revert "arm64: Increase the max granular size"
Date: Thu, 6 Apr 2017 12:52:13 +0530 [thread overview]
Message-ID: <4525901c-45d4-6bd8-eec6-ae92977f16d1@codeaurora.org> (raw)
In-Reply-To: <10fef112-37f1-0a1b-b5af-435acd032f01@codeaurora.org>
On 4/5/2017 10:13 AM, Imran Khan wrote:
Hi Catalin,
> Hi Catalin,
>
>> From: Catalin Marinas <catalin.marinas@arm.com>
>> Date: Mon, Mar 21, 2016 at 10:44 PM
>> Subject: Re: [PATCH] Revert "arm64: Increase the max granular size"
>> To: "Chalamarla, Tirumalesh" <Tirumalesh.Chalamarla@caviumnetworks.com>
>> Cc: Ganesh Mahendran <opensource.ganesh@gmail.com>, "will.deacon@arm.com" <
>> will.deacon@arm.com>, "linux-arm-kernel@lists.infradead.org" <
>> linux-arm-kernel@lists.infradead.org>, "linux-kernel@vger.kernel.org" <
>>> , "stable@vger.kernel.org" <
>> stable@vger.kernel.org>
>>
>>
>> On Fri, Mar 18, 2016 at 09:05:37PM +0000, Chalamarla, Tirumalesh wrote:
>>> On 3/16/16, 2:32 AM, "linux-arm-kernel on behalf of Ganesh Mahendran" <
>> linux-arm-kernel-bounces@lists.infradead.org on behalf of
>> opensource.ganesh@gmail.com> wrote:
>>>> Reverts commit 97303480753e ("arm64: Increase the max granular size").
>>>>
>>>> The commit 97303480753e ("arm64: Increase the max granular size") will
>>>> degrade system performente in some cpus.
>>>>
>>>> We test wifi network throughput with iperf on Qualcomm msm8996 CPU:
>>>> ----------------
>>>> run on host:
>>>> # iperf -s
>>>> run on device:
>>>> # iperf -c <device-ip-addr> -t 100 -i 1
>>>> ----------------
>>>>
>>>> Test result:
>>>> ----------------
>>>> with commit 97303480753e ("arm64: Increase the max granular size"):
>>>> 172MBits/sec
>>>>
>>>> without commit 97303480753e ("arm64: Increase the max granular size"):
>>>> 230MBits/sec
>>>> ----------------
>>>>
>>>> Some module like slab/net will use the L1_CACHE_SHIFT, so if we do not
>>>> set the parameter correctly, it may affect the system performance.
>>>>
>>>> So revert the commit.
>>>
>>> Is there any explanation why is this so? May be there is an
>>> alternative to this, apart from reverting the commit.
>>
>> I agree we need an explanation but in the meantime, this patch has
>> caused a regression on certain systems.
>>
>>> Until now it seems L1_CACHE_SHIFT is the max of supported chips. But
>>> now we are making it 64byte, is there any reason why not 32.
>>
>> We may have to revisit this logic and consider L1_CACHE_BYTES the
>> _minimum_ of cache line sizes in arm64 systems supported by the kernel.
>> Do you have any benchmarks on Cavium boards that would show significant
>> degradation with 64-byte L1_CACHE_BYTES vs 128?
>>
>> For non-coherent DMA, the simplest is to make ARCH_DMA_MINALIGN the
>> _maximum_ of the supported systems:
>>
>> diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h
>> index 5082b30bc2c0..4b5d7b27edaf 100644
>> --- a/arch/arm64/include/asm/cache.h
>> +++ b/arch/arm64/include/asm/cache.h
>> @@ -18,17 +18,17 @@
>>
>> #include <asm/cachetype.h>
>>
>> -#define L1_CACHE_SHIFT 7
>> +#define L1_CACHE_SHIFT 6
>> #define L1_CACHE_BYTES (1 << L1_CACHE_SHIFT)
>>
>> /*
>> * Memory returned by kmalloc() may be used for DMA, so we must make
>> - * sure that all such allocations are cache aligned. Otherwise,
>> - * unrelated code may cause parts of the buffer to be read into the
>> - * cache before the transfer is done, causing old data to be seen by
>> - * the CPU.
>> + * sure that all such allocations are aligned to the maximum *known*
>> + * cache line size on ARMv8 systems. Otherwise, unrelated code may cause
>> + * parts of the buffer to be read into the cache before the transfer is
>> + * done, causing old data to be seen by the CPU.
>> */
>> -#define ARCH_DMA_MINALIGN L1_CACHE_BYTES
>> +#define ARCH_DMA_MINALIGN (128)
>>
>> #ifndef __ASSEMBLY__
>>
>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>> index 392c67eb9fa6..30bafca1aebf 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -976,9 +976,9 @@ void __init setup_cpu_features(void)
>> if (!cwg)
>> pr_warn("No Cache Writeback Granule information, assuming
>> cache line size %d\n",
>> cls);
>> - if (L1_CACHE_BYTES < cls)
>> - pr_warn("L1_CACHE_BYTES smaller than the Cache Writeback
>> Granule (%d < %d)\n",
>> - L1_CACHE_BYTES, cls);
>> + if (ARCH_DMA_MINALIGN < cls)
>> + pr_warn("ARCH_DMA_MINALIGN smaller than the Cache Writeback
>> Granule (%d < %d)\n",
>> + ARCH_DMA_MINALIGN, cls);
>> }
>>
>> static bool __maybe_unused
>>
>>
>>
>
> This change was discussed at: [1] but was not concluded as apparently no one
> came back with test report and numbers. After including this change in our
> local kernel we are seeing significant throughput improvement. For example with:
>
> iperf -c 192.168.1.181 -i 1 -w 128K -t 60
>
> The average throughput is improving by about 30% (230Mbps from 180Mbps).
> Could you please let us know if this change can be included in upstream kernel.
>
> [1]: https://groups.google.com/forum/#!topic/linux.kernel/P40yDB90ePs
>
Could you please provide some feedback about the above mentioned query ?
> Thanks and Regards,
> Imran
>
>
>
>
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a\nmember of the Code Aurora Forum, hosted by The Linux Foundation
next prev parent reply other threads:[~2017-04-06 7:22 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-16 9:32 [PATCH] Revert "arm64: Increase the max granular size" Ganesh Mahendran
2016-03-16 10:07 ` Will Deacon
2016-03-16 13:06 ` Timur Tabi
2016-03-16 14:03 ` Mark Rutland
2016-03-16 14:35 ` Will Deacon
2016-03-16 14:54 ` Mark Rutland
2016-03-16 14:18 ` Catalin Marinas
2016-03-16 15:26 ` Timur Tabi
2016-03-17 14:27 ` Catalin Marinas
2016-03-17 14:49 ` Timur Tabi
2016-03-17 15:37 ` Catalin Marinas
2016-03-17 16:03 ` Marc Zyngier
2016-03-17 18:07 ` Andrew Pinski
2016-03-17 18:34 ` Timur Tabi
2016-03-17 18:37 ` Catalin Marinas
2016-03-18 21:05 ` Chalamarla, Tirumalesh
2016-03-21 1:56 ` Ganesh Mahendran
2016-03-21 17:14 ` Catalin Marinas
2016-03-21 17:23 ` Will Deacon
2016-03-21 17:33 ` Catalin Marinas
2016-03-21 17:39 ` Chalamarla, Tirumalesh
[not found] ` <CAPub14-sFgx=oCHzJPb9h9b_V0rbn5UAMDNJ-yTkjhz38JPqMQ@mail.gmail.com>
[not found] ` <10fef112-37f1-0a1b-b5af-435acd032f01@codeaurora.org>
2017-04-06 7:22 ` Imran Khan [this message]
2017-04-06 15:58 ` Catalin Marinas
2017-04-07 2:06 ` Ganesh Mahendran
2017-04-07 8:59 ` Catalin Marinas
2017-04-12 5:13 ` Imran Khan
2017-04-12 14:00 ` Chalamarla, Tirumalesh
2017-04-17 7:35 ` Imran Khan
2017-04-17 10:38 ` Sunil Kovvuri
2017-04-18 14:48 ` Catalin Marinas
2017-04-18 17:05 ` Sunil Kovvuri
2017-04-19 12:01 ` Catalin Marinas
2017-04-19 13:11 ` Sunil Kovvuri
2017-04-25 6:42 ` Ding Tianhong
2017-04-18 18:21 ` Chalamarla, Tirumalesh
2017-04-11 4:40 ` Jon Masters
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